I recently got myself a Canon Digital Rebel and a 70-300mm IS lens. I fell in love with the IS lens with the very first test picture. Wow, very cool.
Anyway, I took some pictures of aircraft (naturally) on an overcast day on the "sports" setting. They were clear, but rather dark. I've also noticed on sunny day shots, the shadows seem to be darker than what I would consider to be acceptable. I have however, had some great shots come out as well. I intend on getting a polarizing filter soon.
What other tips would be useful for the beginner like myself?