The Kingdom Hearts Dos and Don'ts Handbook

Reflect is really good especially when fighting Sephiroth. I was trying for ages but then my sister told me about using reflect and I beat him ^^ also level up your valor form at an early stage- you will get more hits in when you are weaker so will level up more. If you are having trouble level up and go and find yourself a route with lots of heartless that will get you lots of experience.