Every week (sometimes bi-weekly) the community hosts a server that dedicates 30 minutes at a time to a different custom make in the alpha and beta stages. That way everyone gets equal play-time, and helpful criticism live, as the game is being played. The instructions for taking part in a gameday will always be listed in the thread (which is usually posted a week in advance, maybe a bit later).
But make sure you create a [WIP] (work in progress) thread for any maps you work on, so you can update the community with screenshots and updates you've made to your maps, and allow for discussion about them.