Man I wash my jeans whenever they get more stretched out a bit, i.e. whenever they stop framing my ass optimally, which is like every 2 or 3 weeks or so. When I was working in a barn I was wearing two pairs every week and washing on the weekend because they got so gross, but otherwise they don't need to be washed that much.
You can put jeans in the dryer! It is ok! Animal Ghosts is precisely right about washing them inside out, and you should leave them inside out when you put them in the dryer. The key is to not dry them completely. When you take them out, seams and hems and pockets and wherever else there are several layers of fabric should still be at least a little damp. Hang them up or lay them over a vent or a heater or something to finish drying. Feel free to wear them still damp, too, I guess, but the fibers are more likely to be permanently stretched if you do (as in, they won't shrink back up next time you wash them).
The problem with putting jeans in the dryer is that getting them completely dry usually means you have over-dried them. Denim is 100% cotton, or at least it usually is, and extreme heat makes cotton shrink up. The mistake people make is noticing that the waistband is still damp and throwing their jeans back in the dryer, even though the legs of the jeans are almost definitely all dry, which means that the only other physical change that the heat and the motion of the dryer can make on the denim is to start contracting the fibers of the dry parts.