Read lots of poetry. The best way to learn how to write poetry is to read it!
Always read your poem aloud to yourself once it is finished and ask yourself if there is anything that sounds clunky or out of place.
Play around with your tenses! Try writing a draft of your poem where you remove all the “ing” words – walking could be walk or walked. You can always change it back again and you may find you have shaken loose that one line you couldn't get quite right.
Think about details! You may find you make your poem much stronger by focusing on details which your reader can see and feel.
Finished poems are often the result of many different drafts. Professional poets will return to a draft of a poem making changes again and again before it is ready to share with other people.
Try laying your poems out on the page in different ways. Remember that line breaks will change the rhythm of your poem. Think twice before centering your poem as a wobbly left hand margin slows the reader down and turns every line break into a extremely long pause.