The first thing I'll do is break up the coastline a bit. Here and there I add islands, and provide hints toward river deltas opening out onto the sea.
The mountain ranges provide hints of where streams start, and the jagged coastlines provide ideas for where the riverways end. I've also been given a few rivers to work with, so it's now a case of using a rudimentary understanding of geography to piece these components together. I'm going to use a system where rivers are noted in two distinct types on the map. Wide waterways capable of being navigated by barges and ship-borne traders will be indicated with a double thickness, while smaller rivers and streams will be marked with a single thickness line.
I break up the streams as they approach the designated mountain ranges, this reflects the way real streams join togther to form more prominent waterways. Due to the size of the map I won't bother drawing in even smaller rivulets and creeks, this also gives GMs a bit of scope for their own world development when they create scenarios to be played out on the map.
I can only fit half of the map onto the window for the purposes of tracing the sketch onto the canvas, so rivers, mountain ranges and all the basic layout work is drawn for one half before moving the whole setup across for the second.
If the black lines of the rivers indicate the natural low points in the landscape, where waters flow to, then a different colour will be used to mark the natural high points in the landscape, the ridges of mountain ranges and rows of hills. Because these two are mutually exclusive (you can't have a high point where there is alredy a low point), I can vaguely work out where the ranges are based on where the rivers are not. Then I make things a bit more intereating by ensuring the ranges are jagged with a lot of branching elements threading between the streams and rivers, as well as sometimes just protruding into plains.
The mountain ranges now need to be detailed a bit. Individual mountains are added along the range lines, and a few more branching fragments of range are added in to create a bit more interest and to make the map a bit more "realistic". After all, I hate straight mountain ranges, which is probably a factor of growing up in a mountainous area. I like to see how ranges twist and turn, and valleys meander between them. This will also make it easier to determine where forests and other vegetation need to be placed later.
There will be quite a few elements added into this map as potential story hooks. I have no idea how they will be used, but I figure that I'll add them in anyway, as tools for the other collaborative GMs to use if the need arises.
The drawn map ends up looking like this, but there is still a long way to go, because this map will be a painted piece and not a drawn one...