Was an admin for a few years on a very popular RP server. Could write an essay on this subject honestly. But rather than just stating what makes a bad admin, here's some of the simplest pieces of advice I can give to people in staff roles;
Remember why you (probably) became an admin. At the end of the day, we're all players here trying to engage in this form of entertainment we enjoy. Your volunteer position is greatly appreciated, but it doesn't make you more than your fellow community members. Your role is about supporting the community, not controlling it. Players first mentality. Similarly, non-staff players need to remember that the people working in staff roles are doing so voluntarily and are unpaid. They're doing this (probably) out of pure passion and it's a lot of work. Respect goes a long way with a staff member, because we do really appreciate it.
I always had a simple rule. If you treated me with respect, I'll do the same. If you don't, I will treat you like shit.
Don't be afraid to not know everything. Too often admins become complacent or believe that they know everything about a subject. There's nothing wrong in asking people, particularly non-staff, for information. For instance; many don't have the in-depth knowledge of Motorcycle Clubs and how they work in the real world. But there are people who do have the knowledge and experience and would gladly share. It doesn't make you any less of an asset to the community to ask for help.