Given the level, there is a variety of instructional material that targets each of the levels. Most of those materials suggest by content and in sequence what should be presented at the respective level (usually Levels 1 through 4). Some of the popular materials with which I am familiar are English In Action (Thomson-Heinle), Exploring English (Longman), Focus on Grammar (Longman), Grammar In Context (Thomson-Heinle). There are, of course, "tons" of supporting materials as well as on-line facilities. I hope this helps.