To Get 100 sneak, Go to high broth gar with a dagger, find one of the greybeards meditating or whatever, sneak up behind them and his them, don't hit them too much because you will be turned into an ice cube in seconds. I got from lvl 20 sneak to lvl 100 sneak in about 20-30 mins. Your sneak will level up about 1 every 2-7 hits.

To get free training (it's easier to do it when the person yo are getting training from is your follower) simply ask them to train you, then pickpocket your money back. If they are your follower however, ask to trade some things with them then take your gold :3

Hope this helped, let me know if it did. Thanks!