use your favorite body part as a reward for doing a great job on chest and bis....
Ie Go to gym, and the first thing you do is chest and bis, Once you have completed your goals for that exercise, what ever thay may be 30 usefull, controled reps, or increased your weight on the last set etc.
Then do Bis, and teh same thing, again 3 useful sets, or 30 reps, or weight increase.
Then go do some squats, bent over flys.. I find a lot of people dont like doing teh exercise they are not as good at.., their good exercise seems to give them more rewards as they are traing them harder, and more frequently..
By working your favorite muscles last you will be more tied, myabe not quite as strong, but it will encourage you to focus on them, more so you can get to what you want to do, it will take some self disipline.
I was the complete opposite, I Looove chest, and bis day, you leave feeling so much bigger...but my legs are weak as a result. But I have focused now on doing a dedicated deads, or a dedicated legs day. No excuses, legs or back are the focus so I get in and smash em, no dribbling off to play with the bench..bench is out of bounds that day..