Chest
Run the band behind your back, lie down, press up like a flat bench press. For better results, let the hands cross at the top to squeeze the pecs.
For more scapular movement, do this exercise standing and use a shorter band - I now use 32" bands.
Some people say that you cannot isolate the lower or upper chest. I say, bah humbug. Exhibit 1: Franco Columbu - one of the finest chests in bodybuilding history. Resistance bands let you focus the direction of force very precisely. Your body is smart and will activate the muscle fibers that pull in the right direction. This is the most direct way to develop your upper chest fibers, once you find the right angle.
Loop the band behind your back, hold in both hands. One hand is extended forward / down, the other hand moves slightly upwards across your chest, until your upper chest is fully contracted. Adjust the tension by more or less extension of the inactive hand. Alternate sets with the left and right hand. Power should come from your chest and front delts, not your triceps. Think hinging at your shoulder, with your elbow angle not changing much.
Same as above, but your active hand moves down, until the lower chest is fully contracted. For this version, I lock out the arm at the end of the movement to nail my triceps at the same time.
Triceps
Lie down on your side. Hook one end of the band on a foot, the other end in your hand. Start with the arm fully bent, with your triceps fully stretched, hand near the base of your neck. Straighten your arm against the resistance of the band. You can vary the tension by extending your leg, or keeping it slightly bent.
Hook the band to a high attachment point, e.g. a pull-up bar or a door anchor. Push the band down and apart, squeeze your triceps at the bottom.
If you are big enough, you can loop the band behind your neck, and push down from there. For me, the active range of motion is too small.