Formal:
* Nous sommes prêts. (This is the most literal and formal translation.)
* Nous sommes à votre disposition. (This means "we are at your disposal" and implies that we are ready to start something.)
Informal:
* On est prêts. (This is a more casual way to say it.)
* C'est bon, on est prêts! (This is even more casual and means "Okay, we're ready!")
Other options:
* Nous sommes prêts à partir. (This means "We are ready to go.")
* Nous sommes prêts à commencer. (This means "We are ready to start.")
The best way to choose the right phrase depends on the specific situation and your relationship with the person you are speaking to.