Back when I was riding motorcycle Observed Trials in the '70s, brakes were snuff tin sized drums and were often submerged in one section and then sorely tested on a tricky downhill in the next. Those of us who knew how to get the most out of them got fewer bruises. I ran drums on my 1st 3 tandems because rim brakes weren't very strong back then. Now with Roller Cams, V-Brakes and Maguras, I wouldn't bother.

"Mushy" brakes are caused by flex in the system, mostly the shoes. The best way to eliminate this flex is to ensure that both shoes come into full contact with drum simultaneously. With mushy brakes, if you back off the cable adjustment until there is no drag, you can't pull enough cable to apply maximum force.

1. If brake is new.
Squeeze the brake arm so the shoes contact the drum, and rotate the backing plate in relation to the drum so that the high points on the shoes become shiny due to rubbing on the drum.

2. Marking
As soon as you remove the backing plate, permanently mark the brake shoes so that you will NEVER switch them. Left & right or top and bottom or whatever. If the arm can be removed from the cam, mark the cam so that you will NEVER install it 180 degrees from its original position. As the movements are so small inside the drum, the fact that the cams aren't *perfectly* symmetrical means that a perfectly functioning brake can turn to mush by simply flipping the cam over.

3. Shoe Fitting
Now disassemble the brake, wiping off 99% of the original lube. from the cam(s) and pivot(s). If the brakes are used, and are evenly shiny all over, then they were probably already working pretty well and all you need to do is break the glaze with some fine (120 grit or so) sandpaper. If it's new, or used but not evenly shiny, sand down the shiny spots with fine sandpaper backed up with a flat metal bar. I use a file. Remove very little material.
Reassemble, without the springs. Repeat Step 1 to put new shiny spots on the shoes. Sand them down again. Repeat the process as often as necessary, until the whole shoe gets shiny. When the entire shoe is making even contact, then the shoes don't flex as much and don't feel as "mushy".

4. Lube
Disassemble everything including cones and bearings. Clean out everything and put fresh grease in the bearings, and sparingly, on the cam and pivot. Be careful not to get any on the brake lining surface or the drum. If you do get some on the friction material remove it with electrical contact cleaner spray. I used a soap or PolyUrea based wheel bearing grease, which is more resistant to high temps than the petroleum based stuff. I did some testing which convinced me that it was no more vulnerable to water.

5. Centering
This is the part that is hard to describe verbally, so please bear with me. The results are worth it. The goal is to ensure that when the shoes are expanded, they are perfectly concentric with the drum. Most drum brakes have an unthreaded hole thru the backing plate, which the axel passes thru and a nut on the axel to hold the backing plate in place. This hole is a bit larger than the axel.
What you need to do is make sure everything is concentric when the nut is tightened. Install the wheel and brake on the bike with the nut slightly loose. If you have a non-QR axel, tighten only the axel nut on the side opposite the backing plate. Install the cable and lever. Rotate the wheel, by hand, in the direction of travel while gradually applying the brake. Did I mention that this part of the job is easier with 2 people? With the brake lever squeezed tight, tighten the backing plate nut with a cone wrench. If everything goes right, everything should be in full contact and the shoes should be flexing very little.