Ian 'Mr' McNeilly wrote:Read a lot. Write a bit. Read a lot more. Write a bit more.
As David would say, 'Just my take'.
Learn the rules of English grammar. You don't have to learn them off by heart, as a foreign speaker of English would, but familiarising yourself with them is a great help.
My generation of school kids was not really taught detailed English grammar, because, I believe I'm right in saying, the education authorities thought that once you knew the bare basics, you would pick the rest up intuitively as you read and wrote and learned. Anything more than the basics, they opined, was a waste of time.
I disagree. When I came to Russia, the job I had lined up went tits-up and the back up job I had did too. I decided to start teaching English and was amazed how little I knew about English grammar. How many of you, for instance, would know when to use the present coninuous and when to use present perfect? Do we all know what prepositions and particles are?
Most of the time, as a native speaker of a fair writing standard, you can 'feel' when it's right and when it's wrong. But it's better to know.
Eats, Shoots and Leaves is a nice starter for the basics, and beautifully written itself; Bill Bryson's troublesome words is a cracker, and in writing it he may have become the funniest lexicographer of all time. But beyond that, learning some rules would be a good start. My girlfriend speaks 3 languages completely fluently, another to a highly advanced level and yet another to lower intermediate level and she knocks me into a cocked hat when it comes to English grammar -- even though it's not her native tongue.
My own articles weren't exactly to the standard of some posters on here, like James and David, but if I was to advice anything, it'd be that.