Go to the group search thing, type in "literature" and then read the groups' little about blurb. You can usually tell which groups are good by things like what date their last journal entry was, as well as the way they present themselves (ex, do they talk about accepting all work, or do they have a fairly high standard they require in order to accept a submission, or if they have a specific theme you must adhere to).
Then you just ask yourself if you want in a group. Do you want a group with hundreds of watchers? Or is quality more your thing? Do you want a group that floods you with all kinds of submissions, or one that has significantly less? Do you want to watch the group for the quality writing, or just show off your own work and try to get some favs? Do you want the group to auto-accept your work? Do you want a group that provides contests or prompts to participate in, or has a system for promoting critique?
Answer all those questions, then browse the groups and look for things like number of watchers, last update, and what kind of updates, as well as maybe checking out a few thumbnails in their gallery.
Yeah it takes some time but not every group is right for everyone, so it's best you search for yourself.