Found this on the alt.games.warcraft newsgroup, re-posted here:
Credits to Icebrow on Earthen Ring-EU for writing it:
聽A lot of people bemoan the new LFG/LFM interface, saying it's crap, or whatever. It's not it does a marvellous job. However it's so bone-hedadely unintuitive that you wouldn't know this until someone pointed it out to you with an epic staff. So, as a public service, please read this handy guide for using the LFG/LFM interface.
0. The big buttons that lead you to the LFG and LFM tabs do exactly that. They don't change the behaviour of the tool. Just click whatever, and then choose between the LFG and LFM tab as needed.
1. Turn off auto-join in both the LFG and LFM tabs. That puts you in a group automatically, like meeting stones used to. Real people dont like being matched with strangers, they want to see who's joining/who they're joining. What were Blizzard thinking when they were designing this?
2. Only bother with LFG if you're really flexible about where you want to go and want to signal your availability to many different optons. This is like posting "LFG Strat, Scholo, UBRS". Relatively few people do it, and I recommend not using with the LFG tab at all.
3. Regardless of whether you are forming or wanting to join a group, go to the LFM tab. Choose the type of instance you're after and the name, for example "Dungeon" and "Stratholme". Note, LBRS is in Dungeons and UBRS in Raids.
4. Unless it's like 6AM, you will see a bunch of names listed. Those with crowns are partly formed groups going there. Those without crowns are individuals wanting to go there. Hovering your mouse over a group shows you the names, classes, and levels of all the members so you know exactly what the group is like.
5. If you are in fact LFG, find a group that suits you and message the leader for an invite. If you are in fact LFM find individuals that suit you and message them to offer them a place. Bear in mind some of the individuals are just browsing, so mainly if you are LFM just wait and if you are LFG ask to join.
6. Use the comment field to indicate something about yourself or the raid. For example comment on an individual might be "Have T2 set, wanting item XYZ only". A comment on a group might be "Supreme Raiders + PuG, PuG get 10 DKP".
7. If you just close the window, the tool will continue to advertise your LFG or LFM status. If you don't want that (for LFG mostly you won't, and for LFM mostly you will) turn your preferences back to "None" in all the appropriate fields.
There you go. Clear as mud! Happy grouping and enjoy the great functonality that this tool actially provides, if you use it this way.