I am making this post because after years of frustration, I have finally learned how to do it consistently. Most sources say that Papaver Somniferum needs to be cold stratified and have light to germinate and this is basically false. Forget about the cold part, that's completely unnecessary. Get a wet paper towel and squeeze out all the water. Lay it out and put the seeds on top. You can lightly mist the seeds but I don't think you have to. Put the paper towel with seeds on top into a ziploc and seal it. Put the bag on the counter in a bright room in your house. Not in direct sunlight, and keep it at room temp. The seeds will begin to open in 2-3 days.
Then drop those seeds onto the soil in a large pot. Lightly sprinkle some soil over them. Put the pot outside and keep it moist by misting it gently. If it's too hot outside to keep the soil moist, you can put the pot in a shady spot. They will sprout in another 2 days. Then move into the sun.
Poppies thrive on neglect. Don't overwater them, don't fertilize, and make sure that the soil drains very well. You don't want fertile soil for this. They would grow like dandelions out of a crack in the sidewalk and be happy. Just when they first begin to make buds, give them Calmag or something similar. I use lime and bonemeal.
The poppies are the most potent 10-14 days after the petals drop off. Look for a brown line to appear just under the round part of the pod. Look at the photo I posted. Do you see that brown line under the pod? That's NOT the one you're looking for. This brown line will appear ABOVE that line, right where the round pod tapers to it's 'neck'.
For years I tried leaving them out all winter, or putting them in the fridge, and nothing worked nearly as well as this method. Now that you're growing them on your schedule you can grow them in 3 seasons. The seeds are easy to purchase online. Look for one called Lauren's Grape. It's beautiful. In the US it's legal to grow them, but illegal to harvest opium from them- so don't do that.