Assuming the hydraulics are all in order, it helps to have the drums turned and then have the shoes arc-ground to match the curvature of the drums. Also, make sure your adjusters (star-wheels) will turn freely and are lightly lubricated.
To adjust, tighten the adjuster until the brakes are just tight enough that you can't turn the drum with two hands. Go push the brake pedal as hard as you can, then make sure you still can't turn the drum. Then back off the adjuster 3 to 6 notches (you'll need to push the self-adjuster arm away from the star-wheel with a thin screwdriver or icepick before it will turn backwards freely) and hit the pedal again. The drum should then turn, but drag just a little. It may take a few more notches, depending on if you have fine or coarse notches, but do all 4 wheels the same.
That's the only way I've ever been able to get drums adjusted evenly.