Well first of all, don't be on the map bedroom or anything like that because that is REALLY laggy for some people. I recommend using a map like Slate or Skylands...
Second of all, you've gotta make sure that people are able to connect to your server (has to do with your ping number. If you don't have one, it will deny some players from coming to your server. I would test that by trying to get a friend to come)
Third of all, whenever somebody joins, greet them and be talkitive and nice. Nobody wants a boring host.
Fourth of all, use as biggest and lest bricks as possible (more bricks, more lag. less/bigger bricks, less lag.) If people are leaving your server that is probably why. (Lag)
Last of all, make things fun. Be active. Run minigames. Do whatever is appealing to them and you.
Hope this helped...
