The next major issue you'll want to tackle is brevity. Writing in a controlled concise manner allows your readers to focus more on what you have to say rather than how you say it. Now remember that brevity means different things at different times. It's not a problem to go into an involved discussion on a topic if you're writing an article about it. People expect that from an article. But it is a problem if you were to elaborate in a similar manner in a product description. To get a good feel for what amount of brevity or elaboration is appropriate, read through the writing of similar websites or of your competitors. You should quickly get a feel for what's appropriate by asking yourself if what you're reading feels too long, too short or just right.
You will naturally improve your editing skills through simple repetition. As you edit more of your articles, you will learn what your preferred solutions to your own common problems are. But there is a limit to how much you will improve if you work within a vacuum. Once you feel you've gotten the hang of your basic editing skills have a friend, loved one or co-worker review your final draft. Don't just ask them to read it and walk away. Ask them to point out anything they might not like or understand. Ask them to really work it over and point out any weaknesses whether they have a suggestion for fixing it or not. Getting someone else to review your work will allow you to find the mistakes that you can't.