Sunflowers like full sun.
When you plant them, plant each seed about 1 inch deep and at lest six inches apart. These seeds have an 80% chance of germinating so, you might plant two seeds for every one plant that you want. You can always thin them after they come up.
Be sure to water them after planting. It usually takes a week or so for the seedlings to appear. This seems to depend alot on how warm it is. You can start your sunflower indoors. We like to use pots made out of peat because you can transfer them straight into the soil when it's warmed up.
Photo from About My Area
If you are going to grow your sunflower in a pot, it's best to have a pot at least 15" deep. The deeper and larger the better because these plants like to send their roots out, out, out....
You'll want to keep the soil moist and fertilize them every other week. I usually water them heavily once a week when they are getting started (about a month) and then water a little bit every day.