I owe some of the improvement in my artwork to these tutorials. ImagineFX is such a great magazine for putting this information up for us to read and download.
This is just a selection of the downloadable tutorials that are available on their site, but these have influenced me the most. It's a sin not to share them.
Become a Better Artist - http://www.imaginefx.com/02287754332446636545/become-a-better-artist.html
20 Fantasy Art Tips - http://www.imaginefx.com/02287754331230632886/20-fantasy-art-tips.html
25 Custom Brush Tips - http://www.imaginefx.com/02287754333461721512/25-custom-brush-tips.html
Getting Composition Right - http://www.imaginefx.com/02287754331360267539/getting-composition-right.html
Know Your Values - http://www.imaginefx.com/02287754332900114177/know-your-values.html
Hennings 101:Colour - http://www.imaginefx.com/02287754329488438333/henning-s-101-colour.html
Liberate Your Colours - http://www.imaginefx.com/0228