Personally, I close my eyes and try to keep calm, because I try to analysis every hand and every game, so after ~50 minutes I feel tired and a bit exhausted.
I also drink water.
30 seconds before start I check my list with formulas to calculate
equity and the bank chances ( I try to count them myself, without programmes, for example calculator)
I also close my eyes to concentrate
Maybe I do something wrong , I don’t know