I'm usually OK (when I do writing, which is increasingly rare these days...). However, there are some placs where I slip.




In addition to HH's comments, I would add "get someone else to read it". Other people will spot errors in your work (including tenses) far more easily than you will, because you will be seeing what you expect to see, rather than what is there. (For the same reason a programmer should never test their own code - they are more likley to miss the errors).

If all else fails, put it down and ignore it completely for a week or so, then come back to it for a re-read. You may catch more mistakes if the original version is not still fresh in your mind.