When there is no mound in the warm up area, be sure to set the catcher at the exact pitching distance as opposed to being in his normal position 4 feet behind the plate. The biggest early inning issue for youth pitchers who throw from flat ground in pre-game and go to the mound for their first inning is missing high.
The angle of the mound will lead to throwing the ball high if you warmed up at full distance with the catcher set back behind the plate and your adrenaline is also up for the first inning--contributing to being a bit up with your pitches as well.
The best hitters for the other team will bat in the first inning. You don't want to miss high and you don't want to leave your fastball up in the zone for these guys.