One might think that if training for an endurance event, "speedwork" would not be necessary. However, in addition to making your average speed higher even when going at a relaxed pace, speedwork trains your body to more efficiently deal with lactic acid that exercise produces.
I have benefitted from the Total Immersion techniques; see http://www.totalimmersion.net/
The best means I have found to improve pace and endurance without loss of technique is pickups. I start each pickup length with painfully slow turnover, concentrating on being "slippery" and "skating" on each side, getting maximum distance out of each stroke. I gradually increase the rate of turnover while attempting to avoid technique deterioration, until I am sprinting by the time I reach the end of the length. This works best in short course (25m) format, of course; in 50m format, make each 25m a new "length".
Learn to breathe comfortably on both sides. This will serve you well in an open water swim, as there are often waves coming at you from one side, making it difficult to breathe on that side.
Because I live where I cannot bike during the winter, I find that cycling is my weakest of the three disciplines each spring. I am now trying to do more intervals on bikes in the gym, get in as much X/C skiing (skating technique) as possible, and when it is possible to get out for short rides, do hill intervals. Ice skating would be an excellent alternative in the winter, also.
When warmer weather arrives, training should include both high intensity rides and longer endurance rides.
I avoid running injuries by not running two days in a row (runs of less than half an hour can safely be added in between). I find that two medium hard runs and one long run per week are sufficient, and leave time to work on the other disciplines. (Though lately I seem to find benefit in doing at least 10 min. of running on the "no running" days.)
The best way I have found for increasing speed is to do 800m intervals. After a 15-20 min warmup, I do 800m at a pace somewhat faster than my 10k pace, but not so fast that I could not maintain it for more than 800m. After each 800m, I do a 400m walk/jog. Two or three intervals are sufficient the first time; later one can build to where 7-10 intervals are comfortably manageable. IMPORTANT: Intervals are high intensity workouts, and should not be done two days in a row, nor should they be done the day before or after any hard run.
While swimming freestyle, it is important to constantly check one's technique. I continually check to see that my hips are breaking the surface (this is possible only if upper body and head are low), that I begin each stroke with an arm extension that stretches my lats as I am rolling onto my side, that my elbow never gets ahead of my hand during the pull, and that I am still pushing water toward my feet at the finish of each pull (when the hand passes the hip).
Learning to spin smoothly at about 90 cycles per sec. (where a cycle includes a complete revolution of one pedal) is important. The bike seat must be just high enough so that your knee is only slightly bent when the peddle is at the bottom of the stroke. Aero bars should be low enough so that your back is neary horizontal when you are on the bars (tho' if this is very uncomfortable for you, raise the stem a bit; you may be able to lower it after you become accustomed to the postion). If your seat tube angle is typical (i.e. not intentionally built "steep" for triathlon), moving the seat forward 1/4 " at a time (up to 3/4 inch max) will put you into a configuration that will utilize hamstring muscles somewhat more and reduce the discomfort of transition to running.
Get someone to watch you run. You need to avoid the inefficiency of vertical motion. Your head should come close to scribing a straight, horizontal line. Also, have someone watch you from the rear and point out biomechanical problems, such as excessive pronation. Shoulders and arms should be relaxed, and arms should swing naturally. Strive to pick up the back foot early enough that the forward foot is forced to strike the ground under the knee and not out in front.
You may think that warming up before a triathlon is counterproductive, because you will need all the energy you have for the race itself. But a 5-10 min spin on the bike (if possible) and a 5-10 min jog , followed by stretching, can make a big difference in how you perform. Swim stretches, in combination with the aforementioned warmup sequence, will reduce the lactic acid buildup in your muscles at the beginning of the swim.
Some athletes save a few seconds in T1 by attaching their cycling shoes on clipless bike pedals before the race. If you plan to try this, you need extensive practice to avoid losing time and/or weaving while slipping your feet into the shoes at the start of the ride. When setting your T1 area up before the race, use a rubber band or thread to hold the crank arms in a horizontal position until you are ready to mount the bike. (Of course they will break and fall off as soon as you begin to pedal.) This will avoid the shoes catching on the ground, and possibly causing a fall, as you push the bike out of the transition area.
While waiting for the start in an open water swim, get down near the surface of the water and try to sight on the marker for the first turn of the swim course. Note if there is something above the horizon that you can sight on while swimming until you get close to the turn marker; this will reduce the amount you have to raise your head for sighting during the swim.
Be ready early for your start, with goggles (and nose clip) in place. In a pool swim, start out at a pace you think you can maintain. In an open water swim, start out faster than your usual pace, then slow to your racing pace. As soon as you are passed, attempt to draft on the passer as long as you can; the proper drafting distance will put your arms in his/her bubble trail, but will not make you adjust your reach to avoid touching that swimmers feet. If you are drafting in an open water swim, continually check to make sure that the swimmer you are following is staying on course; you will not get any advantage from drafting on a swimmer who is not following a straight line.
When you have rounded the first turn marker, raise your head and locate the next turn marker, then look up above the horizon as you did when sighting from the shore.
In an open water swim, the slightest bit of fogging or film on your goggles will make it nearly impossible to spot markers at water level if the sun is shining from anywhere but behind you. You can avoid this by using a high quality goggle with antifog coating. However, even the best pair of goggles will not remain sufficiently antifog for a whole racing season. Use your best goggles for open water races only, rinsing them with pure water after each use; once they begin to be a hindrance to seeing, either replace them or put on an antifog solution (but be prepared to reapply the solution the night before each race; an application won't function for more than one race). Other things I have learned in open water tris include:
Getting a pretty fast start, then drafting on anyone who passes me (at least until I find they are not swimming in a straight line!). To avoid the the initial crush, I try to start to one side (rather than moving to the back).
If it is not possible to use a restroom/port-a-potty just before the swim start, I micturate [look it up] in my wetsuit just before an in-the-water start (another reason to start over to one side!).
I don't try to get to my feet at the end of the swim until my fingers touch the bottom. (And I bring my knees up gently, because I have gotten leg cramps at this point.)
As you near the end of the bike route, stand on the pedals and give your calves a good stretch. This will make a definite difference in how your legs feel at the start of the run. If you are wearing cycling shoes, loosen the straps and place your feet on top of the shoes shortly before you cross the dismount line (don't wait too long!); then when you dismount your shoes will stay on the bike.
If you feel any discomfort in your legs during the run which might presage cramping or injury, don't hesitate to spend 20 seconds or so stretching and/or massaging the affected area. Seconds lost stretching can save minutes (or even prevent a DNF) later.
(See document "transition.txt")
A well fitting suit that reduces drag to a minimum is important. (Since most triathletes do the bike and run in their bathing suit, comfort of the suit for all three segmens of the triathlon should be considered.) Have a good fitting pair of goggles, preferably a pair which you save for triathlons, once you are sure that they fit properly and seldom leak.
Ideally, you want a bike which fits you properly, is light, and aerodynamic. But the fit is most important. For the more serious triathlete, a light, aerodynamic frame, with light, aero wheels, and light components are valuable, tho' expensive, considerations.
Of course an ANSI or SNELL approved helmet is a necessity.
Sunglasses are virtually a necessity, for protection from the sun, wind, and particles in the air. When choosing a pair of glasses for cycling, check to be sure they don't obstruct your vision when you are looking forward with your head down; also, don't buy glasses which you can see over at all with your head down, because they will allow too much air flow into your eyes when you are in the aero position.
Obviously, anyone who puts in the running necessary for triathlon training and competition must have a quality pair of running shoes, preferably a pair selected by a knowledgeable person and based on information about the runners history, weight, frame, etc.
I am convinced that following a Zone regimen (40% of calories from carbohydrate, 30% from protein, and 30% from fat) is ideal, not just for maximium athletic performance, but for overall health. [http://drsears.com/] This 40/30/30 ratio should be the goal of every meal and every snack. It is important to try to avoid high glycemic index carbohydrates (starches, sugars, etc.) as well as saturated fats. The only time that the ratio should be altered is shortly before and during intense exercise, when easily absorbed long-chain carbs (e.g. HammerGel) can be ingested with plenty of water. For multiple-hour training and races, a small amount of protein should be ingested in an easily digestible form (using a product such as Sustained Energy or Pepetuem from Hammer Nutrition [http://hammernutrition.com] is the easiest way to go).
You can buy insulated water bottles, but I have used the following for years:
Wrap your bottle in a sheet of styrofoam (soft, flexible sheets about 1 or 2 mm thick are used in packing of fragile items), holding it in place with any transparent tape. Then wrap it all with a layer of aluminum foil. Finally, cover the whole thing with clear plastic packaging tape. This will keep its contents cold for hours. (Note: The bottle will now not fit in the tight plastic cages, but will do fine in other cages which can expand a bit.)
I generally have to rewrap the bottle only twice a year.
Before spending a long time on the bike, closely cut (NOT shave) any hair that is on parts of your body that contact the bike saddle. And to avoid infection, wash that same area thoroughly before and right after the ride. Also, wash shorts after each ride.