"Play longer practice games" seems the obvious answer.
What TC do you use for OTB non-tournament?

Have you never played chess for hours? You can do this with blitz games too. Or do you mean how do you effectively use the extra time at tournaments?

Wafflemaster,
I play Chess for 4-6 hours every single day. I play blitz seldom. I'm 54 and like to play very slow. Example: Today, like most every day, I got up at 7:00AM and played til 9:30AM. Before the rest of this day is through, I will play at least 3 more hours.
I like to play G/60 or G45. Please tell me how you get used to sitting for hours in the tournament.