Always have some sort of timestamped photo/video to back up the condition of the property prior to anyone's move-in and also immediately upon their move-out. Through Google Play, I have downloaded the app called "Timestamp Camera Free" provided by Yubin Chen. It works fairly well. It also attempts to geolocate and attach the property address as well to the timestamp. The geolocate works... ehh, so-so.
Also, always have an official move-in and move-out inspection checklist. Have the tenant sign the inspection move-in checklist (which would include generalized condition rating and any specific notes of existing damages or general wear/tear). If the tenant signs off, then anything else that is not on that sheet, you could potentially dispute.
You can consider enlisting the assistance of a collection agency to try to recoup any damages. At this point, you are looking at not collecting anything, but with the help of an agency -- you could get probably close to half of whatever they are able to collect. (Shop around and see if this option would work for you. This does not always fit everyone's needs/goals.)
Another option would be to file a small claims case (unless the damages were out of this world), which may not help at all, and you would further maybe need to garnish their wages.. and so-on.
Something else to consider as well, in addition to this is providing a "unit turnover fee" sheet, basically letting the tenant know what the charges will be if they leave the rental in poor condition (anything from a missing light bulb to replacing flooring).