How did I miss this thread???
Yes, a good basis in drawing is essential. Like many artists, I've taken many formal 'art' classes and was blessed with excellent instructors.
You can read everything there is out there about tone, hue, value, line, edges, composition, etc, but then again I can read the pilot's manual for the F-15E, but you don't want to be along for my first flight - assuming I could even get it out of the chocks!
Assuming you are serious about it, like flying AF jets by far the best and most efficient path to success is formal training and experience and practice - except with art maybe a single-minded devotion to self-study if classes are not an option - the "self-taught" route is possible, but good classes will shave years off your learning curve. "Self-taught artist" is a misnomer anyway ... you didn't make up the information on your own, you just took a lot longer to learn what's been known by others for hundreds of years!
That being said, these days there are many DVD and book 'courses' on any level ... start with drawing. As others have mentioned above, this is your first goal - I can't stress drawing enough. Then apply that "foundation" to working in color, which is something most of us take years to learn. I took formal classes as I said, but it was only after about 8-9 years of working in color that I felt like I was to the point of controlling it on my canvas rather than the other way around.
Right off the bat - here's some excellent sources that *I* like. Some may be harder to find, but they're out there:
Mastering Composition, by Ian Roberts
(A brand-new book - excellent - he also offers a long DVD on his site on the same subject - the book is sort of a follow-up to the long DVD. Composition has broken more representational art than almost any other thing, especially 'aviation art'. Problem is many 'aviation artists' are after accuracy first, and 'art' a distant second. WAY wrong approach - and it will show in the form of amateurish paintings.)
Painting the Visual Impression, by Richard Whitney
(Full of wisdom, but it's like that F-15E manual ... takes a while to understand everything in there.)
Alla Prima, Everything I Know about Painting, by Richard Schmid
(One of America's greatest living artists ... another book full of wisdom.)
Air Combat Paintings, the Aviation Art of Robert Taylor
In five volumes (so far), Taylor's approach to 'aviation art' is art first, aviation a close second. Not a zero-sum game, as Taylor shows. If you can, try and find his books in hardback ... lot bigger paintings to study. Also, Taylor's personally-written narratives in each book are very in-depth about the subjects and his creation process.
Books on landscapes, like those covering The Hudson River School ... check out Frederic Church's (American, d.1900) work, for example. I'd love to see what guys like Church would have done as "aviation artists".
Study the work of John Singer Sargent ... a master of the portrait, though he mostly gave that subject up later in his career, Sargent was a master of the art of "painting", period - no matter what he painted. His approach was like all the great masters - simply paint the object as it presents itself; don't worry about "what it is", per se ... see the forest ... the trees will work themselves out.
Web sources:
http://asaa-avart.org (American Society of Aviation Artists)
(Probably the biggest influence on my art so far ... their crits of my earlier work were bone-jarring, but I deserved it,
and I listened. The annual Forums at 'aviation' venues are excellent fun.)
http://www.ehangar.com
('The' online home for aviation artists and collectors. Well-run and you'll find a lot of like-minds here. I'm one of the forum moderators on eHangar, but the 'well-run' part isn't my doing!

)
http://www.hyperscale.com
(Serious scale modeling site - good source of reference materials and contacts for same ... I've made a lot of friends here over the years. In the last few years, WIX has also become a great source of history and discussion for me.).
Magazines:
Art of the West
(US magazine that is full of beautiful landscapes and figurative art ... one of my primary sources of inspiration - after all, the airplanes are only one small part of 'aviation art'. Look at Robert Taylor and other leading aviation artists ... they place their planes in beautiful complementary settings.
The Artist's Magazine
(US based, with good tips)
International Artist
(very good magazine covering the full spectrum of art)
Hope some of this helps ... there's much more, but the above will get you going.
Wade