There isn't really an easy way. Doesn't matter what you do (unless the breakup is mutual), your partner is bound to get hurt.
If it's about her personality and you don't like it, have some time to discuss it with your partner and what can be done etc. But if you're an asswipe whos found...
1. Don't act like a jerk
2. Don't appear too desperate as to appear like a loser
3. Slight humour goes a long way, but never let it get out of line.
4. Treat her as a good friend.
5. If she isn't your girlfriend yet, never treat her like one.
6. Do not spoil her (gifts etc)
7. Ask her to...
Let P(x) = x2+ax+b , where a and b are real.
i) Resolve P(P(x))-x into two quadratic factors
ii) Find a relationship between a and b which ensures all roots of P(P(x)) - x are real.
iii) Hence or otherwise, solve the equation (x2-3x+1)2-3(x2-3x+1)+1-x = 0