Writers, writing teachers, and editors all say the same thing here: it is extremely important to get feedback from readers before you send work out. Readers will help you see your poem with fresh eyes. They will help you identify all kinds of issues you might not spot yourself--everything from confusing language to simple typos. It's generally best to seek out readers who are more invested in poetry than they are in your personal relationship (i.e., ask somebody other than Mom). But how do you find such readers?
A note about online poetry communities and social media groups:
These can be truly helpful. However, not all online writing communities are created equal. In general, look for forums and communities that offer private critiques set up as exchanges between writers.
IMPORTANT: Do not post work online where the public can see it (for example, on an open poetry forum) if you are interested in publishing it somewhere else. Posting a poem on a public website (including Facebook and personal blogs) nearly always "counts" as publication to journal editors. They want to be the first to present your work to the world if it's accepted, and they won't consider a poem that is already available to the public online.
For self-publication online, see Alternatives to Traditional Literary Publishing.
Is your poem really, truly finished? Here are some tools to help you decide:
The Internet contains vast repositories of conflicting advice on how to select poems for submission--much of it from editors whose recommendations reflect their own policies and preferences. The very best advice?
Read the submission guidelines and follow them, to the letter, every time.