grammar thoughts

My diagnostic score was 82%. In grammar, I don't have many problems, but my current errors were mostly spelling and also run-on sentence. About spelling I just know the rule is to write the words right, and run-on sentence is when you need a coma betwen sentences. About the time writing and revision, it was a little hard to correct my errors, so I just corrected them how I thought they were supose to be corrected. I feel that my current knowledge is okay, but I still need a lot of wrok.