If you style a site by adding bits of css now and again while you build the backend of a site, it will look like crap. I know, because I used to do it, and the work I did then embarrasses me now.
You obviously know what a good design looks like, so do your design away from your project, in Photoshop or whatever, and don't turn it into css until you're happy with it.
Solicit criticism of your design. Ask people who know design to give you feedback, whether you know them personally or online. They'll stop you from repeating mistakes they may have learned from themselves.
Everything the user, heretohelp is saying sounds right to me.
Also, get "the design of everyday things" to unlearn your bad engineering habits.
There are core principles and foundations to design, much like engineering. Cultivating a personal sense of taste is important as well.
Start by doing some reading on the fundamentals of design and typography. Also, start frequenting various design blogs and websites. You need to expose yourself to design much in the manner that programmers get exposed to open source code.
Once you start seeing things created by designers, you'll start to understand what reflects your personal taste and hopefully you begin to develop a coherent opinion.
Give serious thought/time to UI/UX from a functional standpoint. I highly recommend Tufte's treatises on data visualization as a way of thinking about how to model and present data to your users as well.
Next you'll want to begin doing lots of mock-ups, preferably with actual HTML/CSS/JS. Now you can start respinning designs of existing projects you've worked on, and re-do them in a way you're proud of.
Invest enough time, hammer out enough work, you should start producing thngs you can be proud of.
Just like code.
Here's a basic starter page with some information: http://metatoggle.com/design_crs/contents.html
