How many times have you heard bad training advice? Right; there's a lot of it. Here's a quick list, plus some (hopefully) good advice as well.

More is Better.
Maybe not - without rest and recovery, the stress of training just makes you tired instead of creating an adaptive response.

Just Run.
Most other sports emphasises technique, while some runners just run a lot - cardiovascular training is imperative, but poor form can lead to injuries and is inefficient.

Strength Doesn't Matter.
Especially for women and older athletes, and when on technical trails, it does. Strength training can help prevent injuries and prepare you up for increased training load, and aging athletes lose endurance slowly but lose strength significantly.

Train Hard All Year.
The best runners in the world go easy in the off-season. You should definitely keep moving, but recharge yourself physically, mentally, and emotionally.

Paleo Diet Helps Endurance Performance.
While eliminating processed foods is helpful for everyone, ancient humans certainly ate plenty of whole grains and beans. And each individual should do what works best for them. However, glycogen is our main energy source no matter what we eat, especially as exercise intensity increases, so taking in food that is easily converted to glycogen makes sense. "The fat burned during exercise is endogenous." - Hillary (Meaning it's already in your body from various food sources, as ingestion of fat can take hours to become available as energy).

To Acclimate to Altitude, arrive at the race a couple days in advance.
This may be the worst thing you can do. Most people feel fine the first day at altitude, poorly shortly after, and adjust in 3-4 days, and to actually increase your hematocrit level takes much longer. "It takes 19 days to make a red blood cell." - Dr. Tom Hornbein (told to Buzz personally). So your optimal arrival times are 3 hours, or 3 days, or 3 weeks in advance.

There's more! Listen up.