I've done my own a few times and my sisters have always done their own. Not sure if these are good, but...

My mums method for layers works very well for my 4 sisters but I havnt tried it- get your hair into a ponytail high right ontop of your head, put it into a braid and just snip the end of the braid. My sisters get really nice layers that way.
Me, I just cut bits of my split ends whenever my hair grows- I section it all off, then I get my first section and split it up and just cut of the bits I don't want. This way isn't great for getting a hair style, I just do it to get rid of damage and split ends whenever it grows a bit. I do it during de tangling sometimes, it works fine to get rid of unwanted bits.

Just be careful! Anyway, the good thing about curls is its a lot easier to disguise any mistakes than with straight hair I think. I did one side a bit shorter once, but with my curls it was so easy to disguise it.

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