Even if your tires have little wear on the treads, they may not necessarily be safe for travel. Heat and UV exposure accelerate the ageing of tires. This usually will show up as cracks in the sidewalls. The industry statement on life of a tire is 6 years. The modern format for the DOT code is four digits. The first two digits indicate the week number (up to 52) and the second two digits indicate the year of manufacture. Here is a link to an example explanation for decoding the information
ABC's (Abrassions, Bulges, Cuts)
Besides tread wear and aging, tires are subject to the ongoing and ever present road debris. I won't try to make a list of the number of ways tires can get damaged during travel. However, in order to improve the odds of a successful road trip, it helps to start with undamaged tires. I learned to examine each and every tire thoroughly on all surfaces for Abrasions, Bulges, and Cuts. Since there are a myriad of resources on the net, I have linked to a helpful article on what to look for.
Proper inflation seems to be one of the more overlooked areas of tire maintenance. I witness many just using the TLAR (That Looks About Right) method. Sure, it is a quick visual check to make sure the unit will roll without imminent damage. Nonetheless, the only sure method of knowing proper tire pressure is to use a quality (I emphasis quality here) tire pressure gauge. It is necessary to use information specific to your unit for determining proper tire pressure level. It is not a universal number for a given tire, weight, size, etc. There are some variables. Here is a nice tire inflation guide.
Cracks, Bends, Shavings, Lugs
The condition of the rims is another often overlooked issue. Included in this check is the fasteners. It is imperative to have properly torqued lug nuts. Also, it is important to make sure they are all accounted for. With that said, the condition of the rim itself should be inspected. Look for cracks, bends, or shavings. Cracks will indicated the rim is fatigued and is unsafe to use. Bends can be a concern for tire wear, leaks, or vibration. Lastly, shavings can indicate loose lugs. Be sure to include the rims in your inspections.