The left over grass is OK as long as its really dead. I use a set of disks to rough up the soil - and a cultipacker to press the seen into a firm bed. You really want a firm seed bed -(not fluffy soil) for clovers. The chaff can work to help keep moisture in - just make sure you seed heavy enough because some wont get down to the soil where it needs to be for good germination.
My son Helping Culipack.
The little plots are fun - the bigger plots can be a lot of work - but the rewards are maginfied.
Its better to start small, until you have some good success - and then get bigger, and bigger.
Here's a couple pictures of one of the larger clover plots I maintain from this and last year.
2008
2007
FH