This means making sure you have an erection on a daily basis. Lack of usage: To keep your penis in shape and the right size, it is important to exercise it.To get the right size of the penis, always try to avoid these 5 things that can lead to a decrease in the penis size. Read Also: Small Penis Fear 5 Things Make Your Penis Smaller While you may be more focused on the things you can do to make your penis bigger, a few habits might be making things even worse and causing your penis to shrink in size. Here are 5 unhealthy practices that will contribute to the decline in the size and attribute of your penis.