The easiest texas holdem poker tip I can give and I use myself is to always play fresh and alert. As a professional I can outplay most players anyway. But being more focused than them gives me twice the advantage. Taking breaks on a regular basis is important. About 15 minutes every two hours.
Employers do this, not only for the benefit of the employees. But also for the benefit of the company. Employees that have breaks are more productive, less prone to accidents, and produce better products and customer relations.
This is the same in holdem. Less mistakes, better play, and mood. If you had someone playing poker for you wouldn't you want them to take a break when needed? If you are playing to win, taking breaks regularly can give you an edge over players that are equal or even superior.
Taking breaks will also help avoid tilt by keeping you calm and the game in perspective. Things can get hectic in holdem and time away from it can let the dust settle and help you see things clearer. Things that would not be seen in the heat of the moment at the table.
Take about 5 minutes of your break to evaluate yourself or your opponents, the game, etc. And the rest of the time completely away from thinking about the game. Get some fresh air, take a short walk, stretch out or just relax. I have always used this technique and it may be the number one reason for my success besides being a good player.
Something else that I do is try to sit in a game where players are tired and I'm not. This is easy as a full time pro since I can often sleep during the day while my opponents are working. And then play at the same time they do in the evening. This gives me an advantage since they are now tired or will be soon and I'm just getting started! This is kind of a cheap shot. But it's about winning, not being nice. The game is not nice anyway, and nobody is being forced to play. So use any legal advantage you can!
If you have a day job, take a nap before you play on friday night. When you get to the tables everyone else will be tired. Even if you are just playing for entertainment this poker tip will help you win, and winning is always more fun!!