One way to discover usable OIDs is to redirect the full SNMP tree output to a file, find out what interesting and useful information the device exposes, and determine what the OIDs are from that. It's all good as long as the MIB files shipped with Net-SNMP provide the required descriptors, but SNMP MIBs are extensible—anybody can add new information, and many vendors do. In such a case, your file might be filled with lines like this:
SNMPv2-SMI::enterprises.318.1.1.1.1.2.3.0 = STRING: "QS0547120198"
That's quite cryptic. While the output is in the short, textual form, part of it is numeric. This means that there is no MIB definition for this part of the SNMP tree. Enterprise number 318 is assigned to APC and, luckily, APC offers an MIB for download from their site, so it can be added to Net-SNMP configured MIBs. But how?