Many rivers I see that come from mountains come off large water fall's and look UGLY! you don't need that big waterfall to make your river start, why not make it look real?
Here is what you don;t want:
(where the hell is teh water for the waterfall comming from?
(most if not all of this is made on layer 1)
First Step: (first lay grass duh!) Make hill's outline
Second Step: Make smaller ridges comming out of mountains
Third step: Make river outline, have first part start from the top of the map and end at the mountin first drop, then make a second one from base of the bottom of the hill, and end it all the way to the bottom of the map:
Fourth step, take the waterfall tool, and connect the open spots between the river outline and connect the fivers:
Fifth step: fool around with the map tools, add trees, bridges, pathways and plants:
here is one in the snow: