Previous comments are correct in that interaction design/ design is a very deep field. There are some general ideas (Fitts's Law is a very basic one), however I would like to point out that really the user dictates good design.

Do A/B testing, as well as physical user tests. Two types of user tests I find most helpful are the following:

1) Let the user use your website/product but don't necessarily give advice unless he/she is really struggling. Afterwards you can interview them and ask questions such as trouble spots and/or anything confusing.

2) Have a user "think aloud". This is one of my favorite because it allows you to more easily see what is going on in a users head (although its a far from perfect technique). The general idea is to have the user say aloud everything that pops into their head. Anything from "How do I find that link?" to "I liked that feature".

While I don't suggest you do backflips for your users I am also of the opinion that good design can't be done totally behind a desk. You have to get out there and talk to your users!