I would focus on building size and strength. At 14 years old you are still growing and Your hormones should be through the roof so feed your body.
About the height of the bench... You have to do the pull-over across the bench and keep your feet on the ground and you have to stretch it all the way back as close to the ground as possible, if the bench is too high you are not going to be able to reach the floor, but the stretch will still be great.
About bench... if you set a goal for 8 reps but you are not sure if you gonna get there just do 6 or 7 and try the next time.
Leave the pre-fatigue techniques for another tim e in future. By the way the pull-over also works chest that's why I placed it after bench press.
About the height of the bench... You have to do the pull-over across the bench and keep your feet on the ground and you have to stretch it all the way back as close to the ground as possible, if the bench is too high you are not going to be able to reach the floor, but the stretch will still be great.
About bench... if you set a goal for 8 reps but you are not sure if you gonna get there just do 6 or 7 and try the next time.
Leave the pre-fatigue techniques for another tim e in future. By the way the pull-over also works chest that's why I placed it after bench press.