I wish I could give you a prescription to fill at your local pharmacist, one that would raise your grammar IQ automatically. But I can’t.So here are my suggestions. If you are only rusty, then I suggest you obtain a grammar book that would help you with various questions. Next, I would practice writing ten minutes a day without trying to edit the work. This is an important activity, maybe second to brushing your teeth; because the more one writes the better one writes. Finally, if your email program has a spellchecker function, I would definitely use it to review my communications before sending them.