These poppies tend to resent root disturbance, so plant or sow them in situ. If you don't want them to self-seed, then remove the spent flowerheads after the petals fall. If however you'd like another batch of self-sown seedlings in subsequent years, leave the seedheads intact, and when the seed has ripened, give them a gentle shake to spread their contents. When watering, avoid the 'little and often' approach, but when the soil becomes dry, water thoroughly so it can really soak in.