Minecraft wiki entry for Multiplayer_PvP_bases, associated text: Have a hidden mine on the ground to obtain your diamonds and iron.
Make an experience farm, possibly in the End or find a spawner in your hidden mine.
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.
Get resources from the Nether such as blaze rods or quartz.
Recruit people into your faction to speed the process up as well as improve defensibility. You want your base to be manned as much as possible.
Pick a side in whatever is the large conflict is to gain stronger allies and to have someone to fight.
Expand your farms to become self-sufficient. If you want to get animals up there, try putting water in a waterfall. Lead the animals into it and they will swim up.
Build a brewery and make a Nether wart farm, then sell potions to other players for money.