Her is the way we prepare a seed bed in virgin soil, in sandy loam or clay, in our area. First we plow with either a mold board or a heavy disk plow. We plow to a depth of about 6". This is done in the fall for spring planting. The stubble will rot over winter. A cover crop of rye and clover is sometimes broad cast planted on top of the plowed ground. I may or may not allow cows to graze. The following spring the forage will be turned back under with a harrow disk and used as green manure. The soil is usually still soft enough for the lighter harrow disk to work. The green manure breaks down rapidly. After a couple of weeks we may dick again lightly with a drag behind it to level. Some seed requires that the seed be precompacted. If so this is done and the seed is spread on top and the soil is compacted again. Other seed is sown with a drill and compacted afterward.
Having said the above, rye and clover do not require any deep plowing. If you get an inch deep it is more than sufficient for planting. You can get a pretty good stand with no tillage at all. Just broadcast on existing pasture.
As a side note, due to the cost of fuel and the cost of equipment I have been researching systems of planting that do not require deep plowing. For an example there are clovers and grasses with deep tap roots that when they dye off provide the aeration for the soil. Bluestem and others may be able to provide more info. on this type of system.
And yet another note for those that think that the clover keeps you out of using fertilizer. Clover requires a fair amount of phosphorus and potash. If those requirements are not met your clover stand may be way short. Legumes will only produce Nitrogen.