Poppies can grow pretty much anywhere, even indoors. However, they do prefer to get a lot of sun in their lives, so outdoors is always best. If you're planting in a garden, all you need to do is cast the seeds out and let them fall where they may. You can cover them with a small amount of soil, only about a quarter inch, to give them a bit of extra protection from the elements. Poppies don't transplant well, so if you start them off in pots (indoors or out), then make sure to handle them very carefully when transplanting. Peat pots work well for starting out too, as you can plant the pot as well and it will biodegrade. This way you don't run the risk of hurting the poppy's sensitive root system.