For many years in EQ2, I was a casual raider. What I mean by that is, I would primarily run group zones with guild mates but from time to time I would join a pickup raid or tag along when another guild needed to fill some raid slots. Several times, when filling those empty raid slots for other guilds, myself and some of my guild mates were asked if we would be interested in coming along on a regular basis. In one of those cases, I even worked my way up to being one of the raid leaders even though I was in a different guild.
The reason myself and some of my guild mates were able to do this is because we like being good at our characters. We try to get whichever upgrades we can from instances, quests, faction merchants, etc. We make sure all our spells/CAs are Expert or above. We make sure our items are adorned. We try to come up with the best AA spec we can and consult with each other to try and be as good a player as possible.