You'll get better, just like we did. Just make sure *when* it happens you make it look like no big deal and like you meant to fall over!
I'm with Canadian Giant ... it seems to happen to me with no obvious rhyme or reason. I probably fell a few times the first year then went a couple of years without any. Guess what? One year, I fell over like three times (!!!) in pretty quick succession. Been a few years since and I've been able to stay upright (excluding one car / bike incident that was every bit as embarrassing as tipping over but I digress).