Here I would like to write down my ideas about improvement. I experienced these the hard way and would like to pass this experience to beginners. So that they might reach this level faster than I did.
Imho the best way is:
One must know the rules. And reading a book or website about this isn't really encouraging. It's probably easy to ask a friend.
Once you know the rules, you must know master the basics. I strongly recommend playing Igowin for this. He is the only person of equal strength that won't give you bad advice. While playing IgoWin it is important to fully master the principles of "fake eyes.", "connecting stones", "simple endgame tesuji moves". You should be able to handle Igowin at 12k level after a couple of weeks. Play regulary ...
Your first 19x19 game. Play aya and discover that aya plays corners first, then sides then center. Learn how to approuch aya's stones. Approuching is new since that doesn't really exist on 9x9... After 2,3, not more than 10 games you should be able to beat aya.
Time to meet a stronger opponent. ==> This one knows at least some more joseki.
Probably easiest to start out with 4-4 point joseki. These are simplistic. Not that much variations. Download Turbogo trial. Use only the joseki dictionary of it. Computerplayer is worthless.
Search for 26-28k players on kgs. You should allready be strong enough to get a small winningstreak :). Your earlier Igowin experience should have learned you the tactical tricks of double threaths. It's time to discover the power of nets and ladders.
Now you should allready master the net and ladder tricks. It's time to learn some basic fuseki stuff ! Third line vs fourth line, Double wing formations, extentions (height of wall+1), ... A perfect book for this: Opening Theory Made Easy by Hideo Otake.
On gobase you can find any kind of game you want.
Practice life and dead. Subscribe on Gobase and take a look at the problem section over there. They are of much higher quality than www.goproblems.com. Try the Korean Problem Academy. Your reading will also improve.
If you didn't allready, it's time to find answers for all those unknown joseki moves. And when to apply them. Turbogo might help you again here. If not, try to install kombilo on your system. Also take a look on www.fuseki.info .
You allready played too much on the same server. Amaze yourself and play on DashN. A korean server.
DashN is a perfect place to bring your reading to a far higher level. Play problems with time pressure.
You will love his style of playing. Study his games. You won't regret it. Welcome to the 5k level.