I think the vast majority of pilots understand how to operate at a non-towered airport. I won’t dive into it here, but generally, you’ll enter the midfield downwind at a 45 degree angle. If you’re coming from the upwind side, you will usually cross the midfield at traffic pattern altitude (TPA) and enter the downwind, or overfly the field 500-1000 feet higher than the TPA and do a descending turn to establish yourself at the 45 degree entry angle into the downwind. 

People know about AC 90-66C and the recommendations of the AIM, but generally believe that at an untowered field, those are recommendations and that basically anything goes. And while that is largely true, there is an important regulation that people often overlook: 14 CFR 91.126 and 14 CFR 91.127.

Both are basically the same regulation, but apply to Class G and Class E airports respectively. The important detail is where it says:

So this little post is just serving as a small PSA, as I recently witnessed a multi-engine aircraft from a three letter flight school violate this (often forgotten) regulation. They entered on the midfield right downwind, despite left traffic being charted, while also actively having traffic already in the left pattern. While it was not dangerous due to appropriate communication on all sides, it’s just one less layer of swiss cheese to prevent an accident when people in the left traffic are not expecting an aircraft to intentionally violate a regulation by utilizing right traffic.

To student pilots: Remember, this regulation only applies to untowered airports. At a towered airport, please comply with any ATC instruction for different traffic pattern.

To all pilots: As a reminder, the Chart Supplement (previously A/FD) contains the information as to which traffic pattern is charted. Often, the VFR sectional will also indicate this information in the info blurb for the airport, denoting “RP 12” if runway 12 is using right traffic. The most “official” way to determine the proper traffic pattern, however, as per 91.126, is to verify the traffic pattern indication markings near a windsock in the airport environment. Often this can be seen while overflying the field.