https://www.youtube.com/watch?v=UrVH84yd26Y

Feel free to share your advice, or comments if you think I am wrong here. I'll copy paste the shortened point version here:

1. For easiest time recruiting select an active MMO that is steady or growing in their player numbers, that updates just fast enough for players to not to get bored of content too much and at the same time is not overburdening with updates.
2. Always keep ahead of the curve. That curve may be just being at the level cap if you're leading a casual guild, or knowing your own class well (or classes) if you're raiding a raiding or a PvP guild.
3. Be prepared to log into the same game for significant amount of your free time FOR YEARS. There is no "I'm bored" for guild leaders. We all get bored of the games that we play. But if we want the guild to continue, we must still be there.
4. Help must be given. You can't be completely selfless and help everyone all the time, but as much as acknowledging the person asking for help by saying "I'm sorry, I'm busy right now " can make all the difference in the world. The worst possible guild is the one where nobody answers the new players and nobody gives help. New players do not desire to stay then.
5. Guild chat versus voice. I have found that I need both. Be aware that until you have enough members to converse freely among themselves, you might need to "fake" conversations by chatting a lot yourself.
6. Advertising your guild. Different games use different methods, but no matter the game I would advise against invite spam.
7. Standing out. Not every guild has to do this, but having events, or such special quirks that only your guild does, like releasing online magazines helps.