Full sun or near to full sun.
This is a big feeder, they need lots o' water.
To late to add manure.
Add compost, but not too much. If growing the taller varieties, they get heavy, so they need a solid base, don't make the dirt too loose with tons of compost, they will fall over. You can always stake them if necessary.
A friend puts his within 6 inches up against a 6' wide sidewalk, so when it rains, they get all the water that would have fallen in that 6' wide area, that way he directs more water to his 12-15 tall big head sun flowers. He uses lots of compost and manure in the fall. But, he does not incorporate the compost more than 6 inches. He saves the stems for staking peppers the next year.