A rules plugin - https://forums.alliedmods.net/showthread.php?p=931295
Many players join without knowing that it is a friendly server, most people skip the MOTD and go straight in the game, having a rules plugin could make more people be aware of the rules, admins can also force players to open the rules menu whenever.
A commands list - https://forums.alliedmods.net/showthread.php?p=637467
There aren't too many commands to use on the server, but having a small list to show what there is could make things a tiny bit easier.
A chat filter - https://forums.alliedmods.net/showthread.php?t=329816
It can be set to block certain words in chat, gag, kick, ban, etc. This would make everyone's experience so much better.