Do some weight training. Squats and lunges will work your legs and core. If you do them 2-3 times per week you should start feeling a difference after a month.
do shoulder press (not heavy), pull up (lat pulldown if cant do pull up). and push ups. once or twice a week depending on how much you want to gain up there. you can go 3 times per week upper body if you keep volume low
*Im a bodybuilder. You dont have to get nearly as hardcore as me, but lifting weights will seriously improve skiing. it will wake up your core dramatically and your abs will start taking more and more of the beatin' the stronger they get.