Be sure that you had a good night of sleep, because you need it.
I only drink water. No alcohol. This way, I stay fresh and clear. Even after playing for 6 or 7 hours.
I do not wear sun glasses or other "protecting" my face is always neutral. It is nearly impossible to read my face. Only when I have won a hand I smile a little. 😄
Do not play to many hands. I fold a lot. Play 1 or sometimes 2 hands out of 10.
Watch out when you have a pair of Aces. I have beating a pair of Aces quite a lot, with three of a kind or 2 pair for example.
Sometimes, lose on purpose with 2 really bad cards and lose some small amount of chips.
Try to analyze you opponents play style. Tight or aggressive.
Watch out for the "madman" he is playing with bad cards, bluffs a lots. You can lose a lot from the madman, because sometimes they really have a strong had, while you think he is holding nothing.
I also forgot. Power of your cellphone.
You will see that later during the game some people are not very sharp anymore. ( alcohol, or getting a bit tired ) while other players are just warmed up and play better than earlier.
With these tips, witch I always use. I won quite a lot of games in the past.
Finally. STAY SHARP. Try to have some fun to. That is really important. 😄