Athletes will often recognize certain training "truths" but violate them anyways. It is important to have a list of things you hold universal and try to stick to them. Often the rules that you break may be your own. Here are a list of some of my training "commandments."
The greater the training load, the greater the recovery needed to benefit from it- So simple yet athletes will often attempt to train continuosly at a high volume, even after performance fades significantly. You are weaker after a work out and only gain performance after a period of recovery.
Add small amounts of training stress over time- Big jumps in millage, intensity, or frequency are usually what pushes an athlete over the edge and may lead to an overuse injury.
You can't train at a high rate of intensity year round- Sustained high intensity training must be used prescriptively and you will need regular physical and mental breaks from it. This applies to racing too frequently as well. Your body is a machine that will break down if pushed too hard.
Your training performance will dictate your race performance- Don't expect miracles on race day. In order to race the speed you desire you must train it first.
The mind is as important as the body- Athletic talent is only one component of a successful athlete. The best athletes are adaptable, focused, positive, and disciplined. Mental skills count as much or in some cases more than physical talent, and must be trained and honed just like the physical.
A taper is more than a few days rest- It may take weeks to shake out residual fatigue build up from a peaking phase. The taper is a mix of art and science, and is individualized. For ultra endurance events reducing training load the week before a race is not enough to facilitate full recovery and PR performance on race day.
Specificity is the first rule- You don't effectively train the bike by running, or skiing, or cross training. The best cyclist are on their bicycles; a lot. Peripheral training such as strength training may be important, especially for injury prevention, however your prime objective is to prepare specifically for the race conditions, distance, and intensity.
Periodize- Periodization simply means stair stepping your training stress in small increments that lead to big gains. The top of the stairs is not your goal race but the taper just prior to the race. There should be regular small steps back along the way (recovery weeks) to allow your body to recover from training macro cycles.
Define your limiters- It is possible to be very well prepared physically for a race but still have a disappointing race. Nutrition, pacing, mental skills, even equipment maintenance are all part of the race process and it is important to identify and address what is holding you back.
Be adaptable- Even the best laid training plans will need adjustment and modification as life intervenes. Don't write your training plan in stone and if you miss a work out don't attempt to push too much training volume on a single day or week end. Adaptability also means not training when you are sick or extremely tired.