Here are a couple of publications to tempt you:
Finishing Scale Ship Models: Detailing and Painting Techniques
by Tom Gorman, Chatham Publishing, UK
Painting Model Boats
by Rick Eyrich, Traplet Publications (one of their 'Modeller's World' series), UK
I haven't read either so can't comment on their relevance but subject matter looks right and the authors are pretty well known in modelling circles. My own learnings have come from books on railway modelling, particularly the "noble arts" of weathering and diorama making.
Best advice I've ever had as far as painting goes - practice, practice, practice...
oh, and while airbrushes might not be essential, they can be really useful
Tony