There are several books on how to learn serbian in russian but those won't be a help for you  coz u don't speak it.I started learning basic grammar by them but I've also found many friends from there so i started communication right away and really i didnt have much trouble with it. Of couse i had an advantage that russian and serbian are quite close but still they are very different and if u didnt' learn serbian u wouldnt understand it. First of all u should decide what alphabet are u going to use...probably it wolud be latin. There are several different letters from the latiin english so u just have to pay special attention to those. In fact, find some peeps from the balkan that would be really helpful!

WOW.....thank you people for all this great tip you give me really.........
and thank you "PROF" for all the trouble
but any way i stell need to have a way to learn.........i have to learn people......really  i need to you
and thank you all

 If u love something U can do it very easy, but general Serbian language is hard cuz of cases, if u figure it out, U will know serbian as well. Different between Serbian n Bosnian is that in almost nothing, who knows Serbia, he will know Bosnian too :) They r so beautiful ^^ 

Serbian is not an easy language to learn,however It is not impossible.
 You should start with ,ofcourse,basics,like Serbian alphabeth and pronunciation of the sounds.You will notice we have sounds that are not to be found in any other languages,except maybe Russian.Then you should go through grammar books to get an idea of the language.
If you were planning to learn Serbian by yourself ..hmm..not an easy job.I think you need tutor.
Differences between Serbian and Bosnian are minor and you should not be worried about that.