I had so much trouble cloning at first that I started to wonder wether it was a myth lol. Once you've sussed it though.. its hard to get wrong ever after. My 2 tips that were holding my sucess back are:

1. Give them a good 2 weeks to start forming roots. A lot of people think that after a week they should be rooted but unless ur using aeroponics... give 2 weeks.

2. LEAVE THEM ALONE. Hehe. I know how tempted you get to see if any roots have grown. I used to dig them up very very gently to have a look. Don't! The day I stopped doing this... the day I started to succeed.