I made the error of looking over my Red Planet entry the other day. I was horrified at how many glaringly obvious mistakes there were. HORRIFIED!
In spite of having gone through it thoroughly (or so I thought) several times - it was only after it had been sent off that I realised just how many stupid, blatant mistakes there were.
You'd have thought I'd have learned from previous errors to really check it properly this time. (The last dire error I made was when I'd just got some new software and failed to notice that it hadn't imported to PDF as I'd thought it would (lesson learned - make sure you know how to use your software correctly!)
What I should have done was to print it off and then go over it again. It's amazing how mistakes are easily overlooked on the screen stand yet stand out like throbbing sore thumbs on an actual physical page.
Better still, get someone else to read it - fresh pairs of eyes that have never seen the script before will have a better chance of noticing anything out of place/errors/spelling mistakes etc.
I must now, obviously go a stand in a corner and hang my head in shame for several weeks.
So before you send anything off remember - check, double check, leave it for a couple of days then check it several more times!
Then check it again!