First thing, when dealing with a ouija board, is to say a prayer of protection to whatever god you believe in. Even if you don't believe, the invocation helps.
Second thing, when you are done with the ouija board, you say goodbye to the spirit and repeat the invocation.
Those are the basics. The least unsafe way to it involves creating a physical ring of protection using things like candles and whatnot, which is usually beyond the average person's suspension of disbelief. The "Oh, come one, this is silly" moment.
Ouija boards are not to be taken lightly.
Do some research:
http://ghosts.org/ouija.html