Your style is a part of you. You might say that your style is like mine, or Tolkien's, but it is really only your style. Maybe your particular style is better than mine. Maybe you are so good that people bow down to you in the street. Maybe you are so good that people say that they draw maps like you. You tell them that no one draws maps like you and to get up out of the mud, got it? Style is nothing to flaunt. Let people admire you, don't force them to. Trust me, I wouldn't like it if you came into the room one day and told me that you were better than me. Try to copy someone's style, but recognize the presence of your own creativity. A person in the street should be able to say "Oh! That's one of Bobby's maps!", not "Now is that Sue's, Tom's, or Bobby's map?" 

Stick to one style 

Coherence in a map is one of the prime goals of it's artist. You want your mountains to look like the other mountains, to a certain degree. Uniformity is to be discouraged, but make sure that your map is pleasant enough. A well designed map will have that aesthetic appeal that draws people into it: it should be a story in itself, not just a reference. Look at layout for ideas on how to keep your map looking good. But be sure to remember that it is the little flaws and differences in a map that make it personal. That is why fantasy editors hire a person to make maps: a computer generated image is only good so far. 

Teach yourself 

Teach yourself what you like to do with your maps. If you like to place mountains in a way that is contradictory to someone else's style, go ahead and do it. Forge ahead into previously unexplored areas of your map and change them to suit you. After all, the map is really meant to please you. I do not know of an artist that painted pictures that he didn't like. If you do, then you are more enlightened than me. 

Some rules are definite. 

There are, however, some rules to mapmaking that apply everywhere. For instance: do not make your mountains three inches tall and 3 centimeters wide. Just use common sense. Rivers always follow the river rules, unless a magical force or something is holding them at bay. 

The expirement: 

Now comes the test of your skill. Find a book that you have never read, and that has a good (or not so good) map. Make sure that you do not study the map in detail: just glance at it. Now comes the hard part. Tear the map from the book carefully, making sure not to rip it in half. Be sure that the book is a cheap soft-cover, and not a first edition Fellowship of the Ring. Normally I would be appalled at the thought of mutilating a book in such a way, but it is necessary. Quickly now, make a rude sketch of the map, tracing it's features through your
memory. This sketch should show the placing of mountain chains, shorelines, and maybe some forests. Rivers are not required, as they are very hard to remember. Now, read the book a few times. In the mean time, practice your maps. Anything will do. I usually go off in a corner and jot down a new little world, and then work off of that. After reading the book for the third time, trace your way through it and add to your map. Once you think the map is complete, revise it and compare it to the real map. What went wrong? What went right? Why? If you wish, practice this a few times. It is only really necessary once. 

(note: by the time you complete this expirement you should have run through this entire guide. You should be good enough to produce an acceptable final draft.)