Well, first find a base with part of it unclaimed. this may be hard, but it is very possible. Come with a iron or higher pick, preferrably diamond for some people make their base out of obsidian. When you find one, check if any of their clan members are online by doing /f who [CLAN NAME HERE]. if no one is online, proceed. It's easy to do this, but there is high risk of a clan member coming online. If this happens, you're screwed. All you have to do is mine. if your pick breaks, go to your base and make a new one.Just keep mining. When there is no unclaimed area left, you'rre done!