Don't over use brushes. Brushes are meant to be little
accents most of the time, it gives the graphic more depth
and interest. If you bog down a good blend with brushes,
that can get really scary. Now, just to prove that I am not
without fault, here's an example of what I did one
Try to be individual as possible! I know it is hard when you see a great piece of art it's hard not to want to better it , just go on and do your own thing.
When making affiliate codes (100x35px) Try and not use curly fonts. You have a very small amount of space to put your site's name on there, so try and use small fonts. Yes, there really are pixel fonts! You can look at an overwhelming amount of fonts to download at http://dafont.com.
When making a layout, try and make your colours match as best you can. For example, if you have a header graphic that has mainly blue/green colors, don't make your background color, tan or something that clashes pretty hard. Try and find a blue/green color that you like that just might be on the graphic itself. It will really pull everything together.
When you've made your graphic, save it at the highest resolution you think is reasonable. I hate seeing really beautiful graphics that are pixilated or splotchy.
Try and avoid typos in your graphics, that can be embarrassing, I would know, I've done it and still do it.
Try new styles as often as you can. It's fun, and not to mention you can really get al ot of positive feedback.
Don't use the same pictures over and over again unless you're making an updated version of a graphic.
Don't be a people pleaser, if someone(s) is saying a lot of bad things about your art, move on and don't listen to them.
Use easy to read fonts, this includes effects and colours.
Take into consideration other people's screen settings, for instance, a 900x1200 blend will be huge to a person using 800x600 and lower, but probably would look pretty nice on a 1024x768. A popular blend size for 1024x768 users is actually 800x600, so some 800x600 users just may use your blend as a desktop wallpaper, so be careful!
Be sure to put your name somewhere on the graphic to ensure that no one will try to steel it. Another optional choice is placing your name and the date. For example what I usually do is, "By Aly: '07 Do not redistribute" OR "By Aly: 3, 27, 2007 - Do not redistribute" -- that way if people try and copy your work you have the actual date you made it on the graphic itself.