Judging by your post, your writing is better than average already. Browse these forums and note the mistakes. The first step to improvement is taking note of your skills and the skills of others.
You blog is a good idea. As a reviewer on Bytten, my English has improved a lot since I was effectively forced into writing regularly. Volunteer for something similar, or submit articles to online journals (not necessarily about games, any hobby or interest) and you will improve.
Poetry is actually good practise. Force yourself to write a poem a day for 2 weeks! I guarantee the fourteenth will be better than the first.