How to Choose the Right Index Funds for Your Portfolio

Susan writes in and she says, I'm one of those rare birds that's great at saving. And that is rare. My problem is I'm terrible at investing. I've tried expensive brokerage houses and I've felt ripped off. Now I'm thinking of an index fund, but how do I pick a few to diversify? Do I go international bonds, U.S. based, all three? Where should it go?