My only advice is grammar, grammar, grammar. I mean actually reading grammar texts from cover to cover. It's dreadfully dull but if you don't get a grip on it you won't progress.
You are right Sperk!!! I need to READ the grammar books, cover-to-cover; just like you say.
I have totally run out of excuses... Got to do it now...
It can't be any worse than some of the books I read at university and I still remember some of that.