As you guys have already discussed, painting figures is an important, and sometimes highly personal, technique that makes a huge difference in how they turn out.
One of the things that I do with figures painting to make them look more realistic is to use special brushes that I've cut down for the purpose. For things like buttons, eyeballs (even irises if the scale allows), some of my brushes consist of only one or two hairs. To steady your hand, rest it on top of a padded rest or even your other wrist, so that only your fingertips can move. The piece being painted can be held in some sort of clip or vice under a magnifying glass if that helps you.
Another thing that's often overlooked though is drilling and cutting. The drilling is simple, I use a very fine drill to hollow out such things as the nostrils and ear canals. Sometimes a glass in the hand can be made from clear plastic sprue (from aircraft and car models) drilled out and then filled with thinned enamel paint.
The cutting is for things like pant and sleeve cuffs, and undercutting lapels and ties (some uniforms, like tankers often wear ties) and around the collars. To do this, I use a hot knife to make the initial cut, and then a scalpel/X-acto knife to smooth out the edges.
Anything like belts, webbing straps, epaullettes and packs should be cut off and then replaced with either sheet styrene, paper, tissue or whatever else will give the right effect. The idea is to create realistic shadow lines that just can't be achieved with painting.
For example, with a soldier wearing a bedroll, I'd cut off and discard the plastic bedroll and make a new one out of rolled up tissue (1 ply), painted appropriately and then bound with straps made of painted paper. Buckles can be made out of brass wire, bent into the correct shape and then hammered flat. Buttons can also be made by drilling and putting brass wire in the holes.
Poll