This is purely from my own experience with grad school:
Make sure you meet the grad program's minimum requirements. Then find the person(s) you want to work with and build a relationship. Ask what is important to them, find out if they're a good fit, show them you're awesome, etc. Then when you apply, they can vouch for you and your chances of getting in go up a lot. It seems to be a who-you-know game more than anything. Naturally, that varies by program. When in doubt, stalk some current or former students from that program.