I would recommend finding a book that shows how Boris Vallejo 'does it'
..the techniques he uses can be used to paint any subject matter.
I got my 'start' into 'pro' status from one if his books ..later I ran across a book by Robert Taylor
and it blew me away that he uses the same techniques as Boris
Short version:
Photograph it (or scan images these days) to get the composition you are looking for.
Use that as reference ..that way all the 'angles' and proportions will be right.
And Ink is correct .. practice.
Things I did for practice ended up being published more often than not
(ie: lotta ink sketches I did for practice ended up in the first Air Warrior manual ..the lil brown book
-Frank