Here's what I did.

1. Look at information that's available outside the game. Like it or not, stuff is out there. Much of it is incorrect and out of date, but much of it is still "mostly" accurate. Search for a piece of gear that looks useful, find the mob that has it, then go try to kill that mob.

2. Find out in game. First you need to play a class or race that gets 100% lore or the identify spell/commune. In other words, gnomes, svirfnebli, bards, conjurers, druids, healers, invokers, necromancers, shamans, shapeshifters and transmuters. Then you basically try to lore/identify everything you possibly can.

If you see someone in the guild that's wearing something you don't recognize, ask them if you can lore/identify it. Then ask them where it's from. This is typically easier for goodie gear, since if both you and the guy whose gear you're asking to examine are good-aligned then he's more likely to let you handle it.

If someone won't let you handle their gear, but you have reason to suspect it's rare and or "very good", then make a note of all the pieces you don't recognize. Later you can try locating them. If you happen to locate one on a character other than the guy who refused to cooperate, ask that second person what it does and where it's from. They may be willing to give you what the other guy wouldn't.

Obviously it helps to have the "locate object" spell/commune so you can find out what mob an item comes from, or what other people are carrying that item. However, if an item's level is greater than 51 then you'll never be able to locate it. So keep that in mind. That said, many "very good" pieces of gear are locatable. Pending recent changes, the classes with "locate object" are: conjurer, shaman, shapeshifter, transmuter. Invokers, necromancers and paladins get similar skills, but they're not as useful in the general case.

3. Log everything. If you only log small sessions where you're identifying lots of stuff, sooner or later you'll forget to turn on logging and then you've lost that information. So just log it all.