Any tips for improving my change leg walkover and headstand?

Question:in case you're not sure, a change leg walkover is e.g. when you point with your left leg and as you're in the air, switch your legs so you come up onto your left instead of right.

i have to get it in a month! =\
i can do it....just. but it is SO bad. i thump onto the floor =]

and my core strength has somehow diminshed. so my headstand is crappy.
any good exercises for core strength?
thanks xo

Best Answer - Chosen by Asker: in case you're not sure, a change leg walkover is e.g. when you point with your left leg and as you're in the air, switch your legs so you come up onto your left instead of right.

i have to get it in a month! =\
i can do it....just. but it is SO bad. i thump onto the floor =]

and my core strength has somehow diminshed. so my headstand is crappy.
any good exercises for core strength?
thanks xo

Situps...pushups...and to get that headstand back up, just do a triangle headstand: put your hands and head down, but bend your knees and rest them on you elbows. Then, slowly raise your legs up...it helps you balance and will strengthen your abs again. Hope this helps!