I have done lots of things
1- I set a daily challenge (it ranged from 10 presses in a row, not talking, getting all work/assignments complete, improving significantly a skill etc..)..for those that accomplish it they get certain points.. easy challenges get 5, harder can get up to 15.. By end of month whomever has most points wins, and i get them a prize.. this could have been a t-shirt, a voucher, something. By being able to always change the challenges i could stress things i wanted more work on, and get them to stay focused on it.. It works pretty good. but when numbers get bit it got hard to manager
2- Along with 1 - i added daily challenges.. so for something like sticking a routine 5 points, completing conditioning, etc.. things that you would want always done in practice, but that don't always get done.. they would tally their points at the end of practice and and add to monthly total
1 and 2 were modeled on basically a the way video games work.. (i used it on boys, not sure how well it would transfer to girls)
3- Gymnast of the week is really good i have to say.
4- I setup a website for the team i was coaching, and posted videos and stuff of the kids on a youtube and club page as they got skills.. they always wanted to be filmed and get stuff to put up on YouTube
just a few things.. Overall thought, goal is to motivate and teach the to find that internal motivation.. So no matter what you use, I suggest change it up every 3-6 months, make sure that the it challenges them to be internally motivated to achieve it,