Seconding @plebpoet's suggestion about getting lost in a bookstore or library (not to mention reading her work); fate and chance are fantastic for discovering poems, in my experience.

But also, poetry is an incredibly broad category. If you've got some poets or poems you already like, that's always a good starting point -- see what subgenre they're associated with, if they write in any particular form (sonnet, villanelle, etc) that appeals to you, etc.

If you're starting from scratch, finding a cheap used Norton Anthology of Poetry is great way to get a sense of the range of poetry over a long period of time. And the website of the Poetry Foundation has thousands of poems, as well as some analysis of a lot of the work.