you definitely want to reduce competition as much as possible, as well as have as much exposed soil as possible. To do this you should have mowed it hard and low several times in the fall and try to expose some soil with some lite discing maybe. Frost seeding is meantr to be a quick, inexpensive way to establish legumes. I know several farmers who preform it regularly for maintaining their pastures and have excellent success (and others that have had limited success) The normal recommended rate is usually no more than 1-2# per acre. Another way to "frost" seed is to do a variation I call mud seeding - spred the seed on the muddiest day (hopefully still some freezing/thawing taking place), where your 4wheeler/tractor does some minor digging and exposes soil to help the seed take. Additional mowings through the spring should help reduce competition while the clover is establishing.