Just want to comment that sometimes it is NOT a good idea to have your agent present. The Buyer's agent is already very comfortable working with her buyer and doesn't need to be inconvenienced by having to wait for the listing agent to accompany the showing.
Also I have to say that some listing agents make the showing very uncomfortable because they have a different personality "style" that may not work with the Buyer's personality.
You may be shooting yourself in the foot if you "require" your listing agent to accompany every showing. Your house should "sell itself" with the correct price and immaculate condition.
1) Make your home "easy" to show with just an hour's notice
2) Sanitize your house so you or a buyer would be comfortable eating off of your floors!
3) no evidence of pets (remove cat boxes, dog bowls, leashes, etc. from sight for showings)
4) painted surfaces should be immaculate and look like they were just painted
5) all kitchen appliances should match, no mixture of stainless, white, black appliances, etc.
6) Less is more--declutter, declutter, declutter
7) empty the garage (put your junk in storage until your house sells)
8) landscaping needs to look like a golf course and Disneyworld -- add some colorful plants