If you know computer programming in general and have a good grasp of HTML, I don't think your problem with making reasonably good looking websites is mainly because of CSS. Some quirks and hacks aside CSS is an extremely simple language.

Making good looking website is design and design is a problem, a wicked problem[1]. These are the steps that I personally take to make okay looking stuff:

1. Look at templates and real world websites in the same field/subject and cherry pick features that you like.

2. Implement the layout and components with only structural css parts.

3. Add/Optimize color/style.

4. Refine layout.

5. Go to 3 if not satisfied.

Or my other approach is to start with Bootstrap or Zurb.

1. Pick A "framework"

2. Build the layout and select components.

3. Refine the framework defaults (in bootstrap, you mostly change stuff in variables.less)

4. Add your own styling.

5. Go to 3 if not happy.

[1] http://en.wikipedia.org/wiki/Wicked_problem

Edit: Indent.