Portraits take a fair bit of practice. Some people can pick up the knack for portraiture and others have to work a bit harder for it. Either way practice will develop your skills further and using photos as a reference of features and proportions is one of the best ways to go.
The one face that you will never run out of access to is your own. Paired with a camera or simply your own phone / laptop, you can create endless reference files for yourself to practice on and to develop a style with.
I did a pair of caricatures based off photos i took of myself just sitting at the desk. Both were taken together and I tried to create exaggerated expressions to further help when it came to drawing out the accentuated features for caricaturing myself.