When choosing what weight to use, you should choose whatever weight will allow you to just complete the number of reps in a set whilst still having good form. (fitbodyhq.com)
You might set a daily goal to perform one more rep in each set you do for that day's chest workout. (sixpackfactory.com)
This is particularly true if you're lifting a lot of weight and only perform 1 - 6 rep reps in each set. (darwinian-medicine.com)