Character presentation drawings can be done in a number of ways, and this varies from artist to artist, and depends on the clients needs.
Depending on how far you take the project we are doing, you could produce a) Orthographics b) Turnarounds c) Character in monochrome d) Character in colour e) Character in situ.
I’m not saying you have to do all of these, (phew!) but if you are focusing on the 2D and not the 3D as I suspect you are, then the orthographic wouldn’t be of any use to you. Neither would the turnarounds (You are left with the last three then.) You will need to include a scale reference that the viewer can relate to, (a graphic of a character, for example.)
My advice would be to get some ideas down of how your character will look, via thumbnails, and then try to plot the one you like most in perspective. This should provide you with a challenge. Once you’ve got that done, you can take it in to your favourite 2D painting package and render the hell out of it!! 
Hope that helps some
MIKE