A good grammar book answers questions a search result cannot explain. English grammar books and dictionaries are found in encyclopaedia and reference and language books.
Keep a good grammar reference on your desk and look up one doubt a day. Small daily corrections add up surprisingly fast.
Language opens doors in study, work and travel. Read something every day, speak or write what you have learned, and be patient. Regular small efforts will take you much further than occasional long study sessions.
Students of language and linguistics should combine theory with real use. Listening to native speakers and reading widely in the language will show you how the rules you study actually work in practice.