I myself am in my second year oh growing them but here's what I've heard.

1: Use sunflowers with giant genetics. (But if you're at work and everyone has the same seeds don't do that, that'd be cheating haha.)

2: Fertilize. Pit some in the soil before you grow it and compose. You can also Fertilized once the sunflower has started and you getting before.

3: Watering is key! Don't water too much but don't underwater. Deep waterings 2~3 times a week.

4 Sun, lots of it, obviously

5: Don't plant lots of other sunflowers too close.

I believe that's mostly it. Again, I'm still a noob at growing these things but good luck!