What is the besy way to remember a poem of by heart?

I personally find that repeating it outloud helps. It takes time and a good memory. I would record your self saying it, then play that back while you read it or write it out, I would also try memorizing it in sections (the different stanzas) this way it is not overwhelming, and learn a different stanza each day. Also try practicing in front of family, or an audience (I also find this helps). Good Luck!