Try going back to what worked in the past. Also, you could try setting up a routine that utilizes more than one muscle group (i.e. train chest with shoulders, or triceps on one day). By doing this you are recruiting more muscle fibers and prefatiguing others, and this will create more growth. With your past experience and your muscle memory you should be able to get back to where you were before in no time with a good bulkng diet.