I'm also currently working on a height map and the advice I can give you is actually Pixie's earlier post in your tectonics thread.
Tectonic activity determines most of the mountain ridges. Where two plates collide, at least one side will always be pushed up. This raises the land and because there's compression, mountains will emerge from these areas.
That's as far as I can help you now. You can always add more mountains (from previous collisions), but these are usually not as high as the fresh ones. (I blame erosion and rainfall)
If you want an example of what I mean, look at this image. I'm placing mountains where [1 and 4], [2 and 5a], [6 and 5b], and [7 and 10] collide.