What these guys said- build your habitat around producing turkeys, not just attracting them 45 days out of the year. Nesting and brooding cover are often the most overlooked aspect of it, but consider this- hens start scouting for potential nest sites in February and March. The gobblers you are after won't be far away. Active timber management, old field management, burns, and food plots all have their place. You really need to assess your property, and the surrounding land (2500 acres or so) to see what's missing. Turkeys do not depend on woods- in the plains, they will roost on telephone poles when they can't find a tree. maximize the quality of what you have to work with.
It is impossible to say what the #1 thing you need to do is, however, because each property is different.