Check your spelling and grammar in your survey!

It's obvious, but it's also very often overlooked. Minor spelling mistakes may not get noticed, but if there are too many mistakes, you will start to look unprofessional.

It is a good idea to get someone else to proof-read the survey for you. It's hard to proof read your own work, since you've seen it all before and it's easy to fall into "skim-read mode".