1. You are not a very organized person...You need to keep track of calls and emails from tenants and handle repairs.  Always return your calls.
2. You didn't collect the first month's rent and the deposit before move-in..always collect certified funds or cash before the tenant moves in.
3. The house is not ready...Clean your property and have any junk hauled away.  The yard should look presentable and neat.  Fix anything broken.
4. You don't have a good lease...Have your attorney review your lease and be sure your tenants understand every word of it. 
5. You don't have accurate bookkeeping...How do you know your rents are coming in and the checks are clearing?  If tenants are late did you charge a late fees?
6. You did not properly screen your tenant....Have your tenant fill out an application, call on their references.  Collect pay stubs and have them show you they can afford the rent.  Visit the potential tenant at the home they currently live in. Do they live in a clean,neat home? Is their car a mess? If they live in a trashed house, how long will it be before they trash yours? You may need to do a credit check.
7. You did not advertise properly...Nice signs need to be put up at the property and around the neighborhood with a number they can call for free information.  Advertise online and in the newspaper.
8. You don't take care of your tenants properly.  Welcome baskets, reward them with gift cards, send a Happy Birthday card.  You need to return your calls and let them know you do care. You want your tenants to stay for as long as possible. Take care of your tenants and they will take care of your property.
9. You are not stopping by and inspecting your property.  Then six months later you wonder why your property is dirty and getting trashed.  Keep up on your inspections, it's YOUR property!
10.  You did not hire a good property manager. You cannot do the previous nine "stupid things" on this list.  If you live in the Denver metro area, go to the contacts page on this site and hire us to be your property managers.