This is especially true if you train chest and shoulders in the same workout or on. Consider training rear delts on back day, when you can emphasize them. After reaching failure in a shoulder exercise, don't cheat to eke out extra reps.
The fact is, you can train biceps or triceps first on arm day, but I much prefer. as in doing triceps before chest or shoulders or biceps before back.. After the order of body-parts comes the arrangement of exercises within a body-part workout.