I'm primarily a developer, but, I do a bit of design off and on, and I keep trying to make myself better.
After some experience and talking on other designers on Forrst, I think I've learned a few things about design that might be helpful to other people that are primarily technical, but, have to crack open Photoshop once in a while.
Don't be crazy
If you're like me, design isn't what you're building your app around, you just need it to look and feel good and intuitive.
So, you've probably looked at amazing web design with absolutely off the wall colors that some how just look right. You could try that, or, taking a much easier route, design with simplicity in mind.
People either really like nutty design or they really hate it. Instead, go with simplicity, which people usually like.
Don't try to use atypical color swatches, instead, use a one or two color based theme.
Read up a little bit about typography. Its actually kind of interesting, and very important.
Again, don't be crazy applies here to. Don't use fonts that are incredibly abnormal unless you know that you're going to somehow pull them off well.
Vector images are awesome! You can scale them up or down without loss of quality!
So, invest some time in learning a vector editor. Even though its a little bit less intuitive than a bitmap editor, it'll pay off in the long run.
Pictograms are fonts that are shaped as icons.
So, instead of icons being bitmaps, they're vectors, so, especially on mobile devices, zooming in won't result in quality loss.
Also, changing colors, size, shadow, etc. no longer need an image editor; you can do it with CSS!
I like the entypo pictograms.
Reward the user
Every time the user does some kind of action, "reward" them with some kind of feedback.
When you hover over a button, it should do something, same for when you click it.
Basically, not only does this let the user know that what they did actually meant something, it also makes your application more fun to use.
So, yeah, that's a couple of things I've gathered from various experiences, but, I would love to learn more. Provide design tips in the comments below :)