I'm definitely not good at spar, but I once tried to learn from someone who was and some of the advice I remember is: Not to wear bulky hats or clothes while sparring, always try to guess your opponents next move, don't just randomly swing your sword hoping for the best (I'm sure that's a given, but I always did that anyways), and obviously practice.

Then again, like I said, I'm terrible at sparring. I started doing really well for awhile, but got bored because I didn't have anyone to spar with. Good luck out there!