You should always choose a Coven that is better suited to what you are practicing or what you want to practice. If you want to practice elemental magick, join a coven that deals with elemental magick. Don't join a coven in which the topics are nothing you know about. Joining a coven can be hard for some and easy for others. To join a coven that suits your practice(s) or beliefs, take a minute to go over all of the topic you practice. If you practice for example, dragon magick and fairie magick, this deals with spirits (you are working with the spirits of fairies and dragons), you should join a coven dealing with spirit work. Now let's say you practice gathering energies, chakra work, and balancing your energies, why not join a coven that has to do with energy work? Of course, you are not limited to these topics. Remember to choose the coven that suits your practice(s) the best. You can learn many new things about the practice. Of course remember to contribute your own knowledge and respect and enforce the Coven rules.
I hope this was able to help any who had/has trouble joining a coven.