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.