My advice is to just start hopping servers. Most servers are listed in the various categories on gamespy (via the multiplayer connection). Try different servers out to test the waters, so to speak. Spend enough time on each one you try to get a feel for the other players that spend time there. If you don't care for a server, move on to the next one. If you do find you like one, write that one on a "keepers" list and check out a few more. Eventually you'll find one that fits your play style and what you want out of the game.
These days, many servers require hak files for new and improved content (the only way to get things made by the community over the years). Some still do not use haks (making the easier to just log into without having to download anything). Either way, the server description should at least give a website address where you can find out exactly what's needed and, if something extra is needed, links on where to get it.
Persistent worlds are probably your best bet for finding others to play online with, since they're generally up 24/7. Some are more populated than others...although population does not necessarily mean one is better than another. Again, look around and explore.
You might also want to browse through the
Persistent Worlds & Multiplayer section of the forum. Lots of good servers have threads going there.
Oh, and just in case you're playing with an older installation, make sure you're updated to version 1.69 and have both Shadows of Undrentide and Hordes of the Underdark installed. The vast majority of servers will be updated to the final version and will use content from both expansions. If you don't have them, I suggest just picking up a copy of
NWN Diamond Edition from gog.com.
Good luck in your search. You will find people out there.