Before going on, check out this video on how high-level fluency is attained.
This video was shot at the Melbourne City Library. They have an excellent selection of Graded Readers. Before you spend hours looking through grammar textbooks, experience English in this meaningful interaction with a modified or original text.
Get over to your school library or public library and ask them to start building a collection of readers.
The Penguin and MacMillan books are great, but I think that the Cambridge series are the best: original novels written for English learners. But remember: only read it if you enjoy it!