I'll throw in a couple of things I have learned in the Tulsa area while trying 2 acres of crimson clover two falls ago, and then this past fall trying 5 acres crimson/hairy vetch combo and 10 acres white/red clover combo:
Just like the OSU people say, the clover really does need to be in good contact with the soil, but not soft soil like that from tilling.
My crimson clover areas that were on soft, tilled ground were thin and where there was much groundcover were thin, and lastly when I got some mist for a few hours followed by a few weeks of dry weather the clover didn't live much. Fortunately, I tried in a variety of conditions and on a variety of days to learn what I could before I plant the really large acreage this coming fall (maybe 50 acres).
I think the drill would help to get the clover seed into the soil to make it survive a dry stretch after germination. Three out of four years this may not be needed, but you never know.
If you don't use a drill, I think you just need to make sure there is LITTLE groundcover and that the ground is well scratched up before planting. Plus, do what you can to make sure you get at least a moderate rain soon after broadcasting, and that you get it seeded by Oct 15 at the latest (I suggest end of Sept).
A place in Collinsville is a really good place for getting clover seed. Can't remember the name right now.