You can find the earning information at the top of the in the medits drop down menu.
Medits are earned for contributing to the community, so there's no cheaty way of amassing them.
I'd say the most efficient way is to play the lotto every 2 days and take the time you look at our forums and see what you can contribute to. Either by helping people with their issues, sharing information, being social or if you have something you'd like say (like you did with this post) you can post your own topics.