If you're looking for a discussion community, choose smaller channels/projects and get aquainted with other regulars. If you're looking to learn things and have technical discussions, the trick is not to just find a good channel... It doesn't really work like that. Try to find things you enjoy discussing and have IRSSI ping you when any channel you're in has that discussed.
Don't be afraid to be the guy asking, "How do I get my laptop keyboard controls working in arch." A lot of time great discussion will pop up from people trying to one-up each other in their perfect answer to that and you will either end up learning things you didn't know, or you can correct someone and others will learn from you. Just don't ask anything google can answer like, "what is 0xDECAFBAD in decimal?"
My favorite freenode channels: #gnu ##crypto ##javascript ##linux #perl #python #android ##math #latex #programming ##electronics