I love growing poppies! They are early bloomers for us in Texas. They're easy to grow as well. Just toss seeds out in the fall and wait. They germinate and start sprouting in late January or early February and then take off from there. I haven't intentionally sown any poppy seeds for the past couple of years, yet I get a bumper crop of volunteers every year, like these in the picture above.
I snip off the tops and turn them upside down in a tall container, such as a large yogurt or cottage cheese container. Twirl the stems to empty all the seeds. Once harvested, spread them out on a paper plate and allow to dry. Store in a paper envelope or old medicine bottle until the fall and toss them about your garden to bloom in the spring.