Sit down with a pencil and draw people. I couldn't afford to go to a still life class (Which is fucking amazing and the #1 thing you can do to improve as an artist), so what I did was just sit in a busy public area and draw the people that went past. It was a great way to improve.
Buy old junk from tips super cheap. Try and find a local arts recycling project, tons of free junk; The one near me makes you pay £10 a year for membership to go in and take whatever you want. Hm, use Tesco or similar packs of cheap printing paper to do 100's of cheap drawings for about £4-6 depending on how many pens or pencils you use, for all the repetitive practice involved in getting better at drawing. Steal from construction sites at night. If you have friends with office jobs ask them to keep an ear open for old technologiezz (monitors/computers/photocopiers/desks) and stuff that gets thrown out, a lot of places replace every few years and just send the old and perfectly working stuff off to tips. Read reviews and essays about art and artists free online, learn why you're make shit and everyone else isn't, and such (tate has a new video archive online which is quite good so far). Getting more skill sets just involves grabbing a book from the library or online and doing what it tells you a few times, then a few more hundred times till you mastered it. Drawing, just like the guy above said. If you go to busy libraries, over ground train stations, coffee shops, and etc, you'll find people who sit still for very long periods of time.
Depends on how you 'express your self' really. Also for more technical stuff you can usually sign up for night school, get a few lessons and access to all their equipment for very cheap. I use to do this when I was into printmaking, can't even comprehend how much a big press would be but I went to all three of the local colleges, but they might let you repeat the same ones again -I dunno, I'm not confrontational enough to let them realise I just wanted their print materials.
I shouldn't reply. There's no point. But I'm passionate about the topic. The simple fact is that without excellent instruction you will NEVER PROGRESS. Why? Because art, and the methods of it, are as elaborate as mathematics.
For example, the following transpired on 5 June 2035
[scene: the beach]
<Young Boy> Hello, Mr! You look really smart. you must be a scientist!
<Einstein> I am. As a matter of fact I'm Einstein clone 3281, my boy.
<Young Boy> Wow, how can I become a great scientist like you?
<Einstein> It's very simple. All you need is a sheet of paper and pencils.
<Young Boy> And elite education, membership in government research circles, and access to private cutting-edge research are of no use?
<Einstein> No use. All you need is pencils and paper.
Yeah, studying light (by studying I obviously mean studying by sketching) will bring insight to all of your work. You could spend 3 years drawing different sized boxes in different levels of light and you'd only improve.