Ask HN: How do I pick up some good design fundamentals

I have been programming for about 6 years now using several languages, but have always sort of stayed clear of any design / interface type of work. There is a nagging feeling in the back of my mind that wants me to become more well-rounded but I dont really know what would be a good starting point. I am looking for some tips regarding a pretty broad spectrum that could be labeled design, anything ranging from html/css to wireframing to making great presentations and colour theory is interesting. This can be considered the equivalent of the "how do I teach myself to program"-question. Its probably relevant to say that I prefer using tools that are available on Linux (Im an Ubuntu user) but if people feel adamant that Windows or OSX are prereqs to doing a good job, that might be an interesting discussion too.