Positive thinking and a clear mind are important.
It's all about awareness, not about worrying or thinking too much. Deep concentration and instinctive play is really important. This means not worrying about mistakes, not being negative, not worrying about the future.
Heres some interesting information from Coach Phil Jackson (Who has done more winning than anyone and at NBA level) that talks about this area:
"Basketball is a complex dance that requires shifting from one objective to another at lightning speed"
“To excel, you need to act with a clear mind and be totally focused on what everyone is doing on the floor.” ”Some athletes describe this as a cocoon of concentration”
“The secret is not thinking. That doesn’t mean being stupid, it means quieting the endless jabbering of thoughts so that your body can do instinctively what it’s been trained to do without the mind getting in the way”
Phil Jackson explains that an area he had to improve with his game and an area he has taught pro athletes was not to have a hyperactive, hypercritical mind. Instead athletes should quiet their judging mind and focus on what needs to be done at any given moment.
One way they do this is by teaching athletes meditation so they can experience stillness of the mind.
“A lot of guys second guess themselves, they don’t know whether to pass or shoot or what. But If I’m open, I’ll shoot, and if I’m not, I’ll pass. When there’s a loose ball I’ll go after it. The game happens so fast, the less thinking and the more you react to what’s going on, the better it will be for you and your team”