Maintaining and improving a server isn't hard. But some people just don't know what to do.
For example, you just got a new bukkit server and your exited about it
and people come on and say "Is this even a bukkit server" or maybe "WTF is this ?" even "I'm going on a better server"
You probably don't want these things happening on your server so I'll turn you frown upside down!

PLUGINS
Plugins are very important for your server. You want at least 20 plugins, but if you want your players to be the happiest
or your server to be the most protected you probably want 40-70 plugins on your server. Half of you plugins should be fun and the other half should be to help or run your server better

RANKS
Ranks are also important, I don't know about you but I use Essentials Group Manager to make my ranks.
The ranks you choose are very important. When I log on some servers I'm a newbie. I don't really like that
I like being a guest or a player or a member and not a newbie. I know it sound rediculous. But i just feel that it's more respectful if your a guest, player member or builder then a newbie.

MAINTAINING A SERVER
How do you make your server stay healthy? Well that's simple just treat your players right and make sure they have a good time. Let's start with treating your players right, If griefing isn't allowed on your server and you catch a player griefing then you ask them simple questions like "Whered you get all those diamond blocks?" or "Why are all the blocks from that building is in your inventory?" Don't yell at them or say "HA I SAW YOU GRIEF YOU BITCH!" no be respectful even if they do break the rules.Now let's see, having a good time, hm? Well if a new player is on then tp to em show them around tell em the rules maybe give em starter items. Make sure your server has PvP Survival, Survival and Creative and make sure they know where they can get to it. Players don't like playing on a server they don't know what to do on. Also help players if they ask for help, help em. But I know what your thinking what if they want help with a structure and the need diamond blocks to build it. Tell em "Sorry, but I am only gonna help you with your items not cheated ones" That's a good way to tell em. Now there's also choosing your mods to look after your server when your gone. Who though? Make sure you know them for along time and they have not broken any rules what so ever. Choosing mods are tuff it mean your giving them the right to ban, kick and jail players and they might abuse they're powers. But its actually easy just choose a guy that has been look after the server even when you were there and make sure your trust em.

RULES
Rules now, can't be too stricked or too little they have to be just right. There needs to be at least 6-7 Rules on your server to keep it healthy. There's nothing that i can say now so lets move on to the next category

MAKING YOUR SERVER POPULAR
It's very simple just post it up on planet minecraft and the mc forums THATS IT
also make sure you have a good banner

MOTD
Messages of the day should have very little detail like mine is War grounds PvP
Yours should be something part of your server like if there was a objective on the server like getting 1000 Diamond blocks you would do "Find The Diamonds Make Some Blocks" of course its very boring but add some color to it and it will be spectacular!

SERVER NAME
The server name reflecs everything on your server in 1-2 words! Make sure its related and about your server. By now your server is pretty good well that's all I know about running a server... Or is it?