Nutshell:
— Study books on the appropriate level!
The selection of books I give below assumes that you already know the rules of Go. If not, please visit my Go Rules page or maybe find another resource via the Alternatives page. The latter also lists some introductory book you might want to look at first, before diving into the more advanced volumes.
Being a beginner, lots of life-and-death study is crucial! I bet that most of your games, especially against strong(er) players, are decided by losing large groups. Or small groups. Or medium-sized groups. The point is, the most important thing in your development as a Go player right now is to improve your skills in keeping your stones alive! After all, no fancy strategy will help you if your groups are constantly dying! Right?
It is hard for me to stress enough how important this is for you right now!
I know that maybe some strategy or opening books seem more interesting to
you now, but studying them will offer you very little benefit unless you
get a solid grip on basic survival techniques first! Trust me. :)
As I have already mentioned in the Playing Tips section, Go is in part a pattern-recognition game. The more patters, i.e. small local positions you know, the better you play! Well, I wish it was that simple. But knowing patterns certainly helps a lot. In a sense, studying life-and-death is also nothing else that familiarising yourself with patterns as they pertaing to life of stones.
But there are a lot of patterns beyond life-and-death problems. The most important of these to you right now are, I think, the basic tesuji patterns. In case you wonder, tesuji are usually translated as "clever play, the best play in a local position, a skillful move, a special tactic" (definition taken from the Sensei's Library.) There are a lot of tesuji patterns, some very very complex and difficult, but do not even try to look into those. Remember: Study books at your level! The basics is what you need now, not the intricacies.
But i will still give you some pointers! In my opinion, the idea is still the same, which is to increase your familiarisation with the local patterns. After working with life-and-death and basic tesujis, you might want to look into some basic joseki books (joseki is a standard sequence of moves, mostly in the corner) and some general entry-level fuseki (i.e. opening) and strategy books.
Looking through the advice i gave above, you might be tempted to see it like "ok, i'm done with life-and-death, now lets leave it and move on to something else." Never think like that! You start your study with life-and-death, and you continue honing this particular skill untill the day you die (or stop playing Go, whichever comes first!) The same goes for all other paths of study.
No subject in Go is small enough that you can say you have mastered it!
The problem with Go literature is that, because of its (temporary, I hope) lack of popularity in the western world, you seldom can simply walk into your local bookstore and buy a Go book. Sad, but true. So what can we do?
Well... one way is to make friends with your local book merchant and ask him to maybe special-order some of the books for you. He might know where and how. But, in this age of impersonal mammoth-sized book stores this might not be easy. Luckily, in this age of fast-and-growing internet, we have other resources to get stuff we want.
So, here we are: just order the books you want on-line. Go to one of the many Go Books and Equippment vendors and get what you need. You can find the links to some of these vendors below. Have fun brawsing. :)