Minecraft wiki entry for Player_versus_Player, associated text: A map. Not only it will help you see the environment around you, but it will also indicate where other players are.
Fully Functional, Armed, and Finished Base: A base is always a good choice in PvP servers. To make sure that nobody will find your base try and base it in an ocean biome, underground. Or…
Skybase: A base floating in the air is difficult to access, especially if it is built above an ocean. It will be difficult to locate and difficult to break into, as long as it is fortified with obsidian. Best when used on factions servers especially, but only if you are smart about laying out land. Just make sure you can access it.
The best equipment possible.