Minecraft wiki entry for Multiplayer_PvP_bases, associated text: Expand your mine and keep hoarding diamonds and iron.
Use your spare cobblestone to make an experience farm.
Sell the spare stuff you don't need instead of letting it clog up your storage space.
Create a faction armory with at least 1 reserved set of armor and weapons for each member.
Create a grinder for your base.
Enlarge your base as you invite more members and gain more power.
Recruit people into your faction to speed the process up as well as improve defensibility, but be careful whom to invite.
Pick a side in whatever the large conflict is to gain stronger allies and to have someone to fight.