The "best" guide really depends on what your learning style is. I think you need to discover that first, but by "level 3" I assume you are referring to your Japanese level according to the Japanese Language Proficiency Test (N3), right? If that is the case, at your level you could start reading easy Japanese texts, such as children's books. You could also watch anime or movies for children with subtitles (Japanese, not English). I have found the Genki series to be quite good as well. At the N3 level, Genki II would be most appropriate I think. Additionally, if you are studying for the JLPT itself, then I suggest either 日本語総まとめ　or 日本語完全マスター as both of these series will give you solid practice for the test as well as a comprehensive vocabulary review. I think 日本語完全マスター is best for actually test practice though, because it gives better, more authentic examples of what you will see on the exam. I this advice helps. If this wasn't what you were looking for, please let me know more specifically what you'd like to use.