What to teach in Freshmen comp?

I feel that everybody has different grammar issues. Especially if they are from different backgrounds such as generation 1.5 students or if they are international students. I believe that best way to approach this is to conduct a diagnostic essay and see what are some of the recurring issues in general in class. For example, are students familiar with academic voice? Are students having speech pattern interruptions in their writings? Are they not familiar with active/passive voice? I would try to find out what the main issue would be for the class as a whole rather than picking at every single grammar issues. That can be reserved for endnotes. Other than that, I would probably try to lean more towards something that will enhance everybody in class such as fragments, passive/active voice by using subject and verb, speech patterns in writing, and perhaps word choices (considering dialect features students can also have this problem).