Read as many senryu examples as you can find. It's tricky because it's difficult to find publications or websites devoted exclusively to this form. Simply Haiku is an online literary magazine that features a senryu section.
Decide on the message you want to convey in your poem. Tap into your experiences with your family, friends, coworkers and authority figures. See the lighter side of human nature.
Pick a central situation, image or symbol. Like the haiku, a senryu doesn't use complex language to convey its meaning. These poems are good training for focused thinking.
Count the syllables in each of your lines. Like the haiku, a senryu has three lines with a total of 17 syllables or less.
Identify your setting in one line and write about your subject and the action in the other two lines. Here's an example from Senryu Karai, the inventor of this form: "Catching him/you see the robber/is your son."
Practice this form of poetry. It looks easier than it is. You have to convey a profound idea about human nature in three short lines averaging 5 to 6 syllables each.
Enter your senryu in a contest or submit it to a literary journal. You could win $100 from the Haiku Society of America. Though Simply Haiku doesn't pay for submissions, it's a nice publication credit to have.