For whats it's worth for me, relaxing is also crucial.
Almost concentrating without concentrating or thinking without thinking. Ha, reading that back sounds like some new age zen nonsense!
I suppose it's the classic don't over think or over analyse.
I and I bet just about everyone has had that occasion where the make 2 or 3 brilliant shots, right next to each other only to 'drop' the last arrow out of the group. Probably not directly caused, but certainly not helped b trying to work out what you did right the last 3 times or by desperately willing yourself to "don't miss this one! Dont miss this one! Don't miss this one..."