A few tips from the folks at Exapta:
1) For firm seedbeds, make sure the down-pressure is sufficient to keep the opener at the proper depth (this is especially important for crops such as winter wheat). For JD 50/60/90-series drills, this usually requires that the rockshaft be sloped downward in the rear (see photo) by 5 – 15 degrees, occasionally 20. (The JD Owner’s Manual is incorrect in specifying it be horizontal all the time, which is the appropriate setting only on mellow glaciated soils.)