It is very important to keep up with your fertilizing and watering regime, especially watering,  as drought stressed plants are quick to shed older leaves.   You do not want to have this happen from here on in.   So, ensure you keep pots evenly moist at all times, and that you continue the monthly applications of a balanced fertilizer such as 20-20-20, the latter, up to mid October.    On the matter of pruning, hopefully, you have already encouraged the plant to grow in a nice, bushy shape with regular, judicious pruning.   If your plant still needs a little shape correction, there is  time for one last pinching out of shoots that do not conform to the desired shape.   But try to do this before end August, and ensure there are three large, fully expanded leaves below the pinch.    

Now we come to the all-important step of flower initiation, which starts naturally by late September/early October.    Poinsettias are short day plants, i.e., they flower during the shorter days of the year.   Actually, studies have shown that poinsettia require 14 hours of complete darkness each day for 6-8 weeks before flowering!  Even very low reflected light, such as from a street lamp, can delay the onset of flower initiation.  If you’re really committed and do not want to take chances on your poinsettia flowering in time, you may wish to provide your own ‘dark treatment’.   Simply position your plants in a corner of your garden that receives absolutely no reflected light, or place in a dark shed between the hours of 5:00 p.m. and 8:00 a.m.   Just don’t forget to return them to full sun during the days!  Remember to start this dark treatment by early October, and keep it up each night for 6 – 8 weeks, or until you see definite signs of colour in the bracts.  Good luck.