As medical writers, we need to constantly practice and sharpen our writing skills to able us communicate more effectively with our readers.
Besides referring to writing guidebooks, reading up some good articles produced from good writers and learn from them definitely helps us to write better.
Well, you may also conveniently find some good general writing tips on the internet, such as from the Daily Writing Tips. Sometimes we do need to refresh our 'memory' on the proper application of even the simplest grammar and punctuation, or learn the 101 rules for writing numbers. Believe it or not, numbers and numerals can be very confusing if not written in the right way.
If you are also keen to learn about fiction writing and business writing, then do drop by Daily Writing Tips to see what they have to offer. :)