We put in a clover lawn at our old house. It was the Oregon clover mix (we are in the PNW, there may be a better mix for your region). Here's what we learned:
1) Yes, you can just overseed it over your lawn and it will slooooowly choke out the grass. Takes several years, looks bad during the process. It was better where we actually removed the grass and put in clover.
2) With the mix we chose, there was no need to mix it with anything else. It said we could, but we didn't.
3) If you don't mix it with grass or something else, you will need to water once or twice a week during the hottest/sunniest stretch of summer or it will brown out. Good news is, it will green back up once the moisture returns.
4)If you don't mix it with grass, then overseed lightly every spring with fresh clover, otherwise you will get some bald patches.
5) Look at feed stores for buying seed rather than lawn and garden stores. We paid an average of $1/lb for the seed at a feed store, where as at the nearby garden center is was $15/5lbs. Seems our local orchards use it as a living mulch, and feed stores stock it cheaper.
6) Clover lawns do still need mowed, or at least our variety did. Mowing about once a month or so kept it looking nice.
7) Be careful if you like to go barefoot, because you may step on a bee!
8) Check with your city/water department for rebates for putting in a water-wise lawn. We got a nice rebate on our water bill from the city.
Overall, we loved it. It was lawn enough for the kids and dog to do their things, but it was green enough so the neighbors didn't complain. So did most of the people that looked at the house when we were selling it.
