For the reader with no time to lose, I'll start right away by telling you which book on Pragmatics you ought to get if you want a good introduction to it: "Pragmatics" by George Yule, because it is much more concise, to the point, covers a lot of ground quickly, deals with the essential.
Now, Levinson's book is a book I read twice, and from which I never retain anything. The first time I read it - entirely - I could not mention anything I had read in there. I thought I was simply a bad reader, but after having studied pragmatics for a long time, I realised that the book was simply not well written. It goes into complicated details too fast, before the reader has any real grasp on the matter, and gets lost in discussions that readers usually aren't able to understand, nor care for.
Typically, I'd say that Levinson's book is an "introduction" written by someone who knows not what it is like to know nothing about pragmatics. And even when you know of the subject, you still find his book rather difficult to follow.
I strongly urge you to consider George Yule's book on pragmatics rather than this one.