Welp, make sure you always welcome new players. Always. They'll see your friendliness and be eager to continue playing. It's one of the biggest keys to keeping players.
Whenever someone asks a question (assuming it's logical), make sure you're the first to answer it. Try answering the actual question fully, and then give your own opinions on what to do from there. Ex: "How do I earn money." >Normal, full answer: Sell things to shops, auction them, vote, or even donate. >Extended answer: Sell things to shops, auction them, vote, or even donate. I know where there's a shop btw. Just tell me if you need to sell anything! Never EVER tell someone to look it up. If you can't answer their questions and you've given your best advice to try and help them, use a phrase along the lines of "You can try using the MineCraft Wiki. It usually has useful information, and it probably will give you more knowledge about the subject than I can.
Sometimes you get illogical questions. Just answer it to the best of your ability and just try to defer from saying anything negative about it. Just shake your head and carry on.
If you have a forum page for your server, always be active there, as well as in game.
Besides that just follow the set-in-place server rules, and you'll be fine. Be flexible with your position (if you get it that is. ), don't just be a uniform staff member. Try to stand out, positively!
Anyways, hope I helped a bit.