If you really want to get anal about the tectonics then there are some tuts and numerous WIPs that go into the subject. But for me, plausibility is good enough. First, I don't make mtn ranges that go in circles or squares or funky shapes...true it can be fun but I just don't do it. Second, I don't make them go all over the place...they follow a clear line and may have a few small branches. Third, I make at least one long mtn chain and a few other smaller mtn chains for "flavor". Fourth, I never put them directly in the middle of the landmass, it looks artificial, but by the same token I don't put them all by the coast either as not all places are fjords. Lastly, I know what other terrain is going in and roughly where I want that and make the mtn placement fit that...ie I'm not running mtns straight across a desert or swamp. In the end, you just sort of develop a feel for it after having done it many times.