I'm not the best gamer - I think you need to be strategic and level-headed, and you need to remain calm under pressure... and I don't really have those qualities!
Personally, I think I am much calmer under incredibly stressful situations, and I've learned to deal with pressure and nerves, which is key to being a performer of any caliber.
What helped me was working with my breathing, specifically, using my breathing to stay sharp and focused under pressure and then cool and calm when the pressure was relieved.
Be like a duck. Calm on the surface, but always paddling like the dickens underneath.
Pressure is playing for ten dollars when you don't have a dime in your pocket.
Under every stone lurks a politician.