Avoid lengthy talks in training (1 min. max).

Avoid long lines and standing around (Boring!).
Always keep the kids moving and touching the ball.
Practice the intangibles that happen in the game because they happen all the time (set pieces, corners, goal kicks, throw-ins, trick plays, kick offs). 
Keep training exciting, fun and upbeat so the kids want to be there and learn.
Get involved with your players; it works!
If something is not working well, it's ok to modify it.
Start simple and in big spaces, then add restrictions and limited space once the topic in understood.
Continue to learn different styles, games and ideas because the game is always changing.
You can't teach tactics without technique (can not work on getting the ball wide or combination play if they can not make short and long passes).

The game is the best teacher!