You hear that? We're nuts :O
I think the 2/3 of the head rule is the same....or you can just use pinheads or 'small crickets' for hatchlings.
I go to Petsmart usually, so I get the 'small' ones. Today I went to a different store and got pinheads, which seem to be fine for my smaller crestie
I think some eat real fruit, you'd need to mush it up or put it in a blender....or just use babyfood
My crested loves banana (watch out for banana due to the potassium) 'mixed fruit', blueberry and peach

These are all babyfoods though.
In the wild, the crested geckos live on something like 90% fruit, but I'm not sure if it differs between adults and juvies. Hopefully someone else will answer