Do you know what your strengths and weaknesses are already? If not, I'd ask either your other stunt group members or your coach for helpful feedback on what you do well and what you could work on. There's only so many hours in a day, so it's better to make use of your time drilling the specific areas you know need to improve, rather than the stuff you're already good at. :)
If you're looking for overall advice, though, building upper body strength, especially shoulder strength, can never ever do you wrong as a base. (Plus, it carries over into tumbling!) There's all kinds of exercises you can do at home that you can look up online, with or without weights.
Another easy thing you can drill at home is learning how to push through your legs first, then let your arms/shoulders finish the movement to get a stunt up. I can't tell you how many bases try to use sheer arm muscle to get a stunt up, and that's just making your life way harder than it has to be. A good, strong dip and drive through the legs will make you much more powerful. Good luck!