My theatrical roots are in physical theatre and I use a lot of physical work in the improvisation workshops I conduct, so I feel like I ought to suggest something, but there are about a million factors colliding in my brain, all of them trying to gain position as the most important part of character physicalization. 

Physical manifestations can range anywhere from subtle to grotesque.  I have a belief that you cannot fully master the subtle until you master the grotesque, so I would suggest starting with extreme physical exercises - contortions, really.  Some exercises use the idea of an animal - if this character were an animal, what kind of animal would it be?  Then take on the physical characteristics of that animal and see what that does.  Feel what it does physically and emotionally.  Character development throughout the rehearsal process will include experimenting with these physicalizations, picking those that feel right and eliminating those that don't.  Then there is a process of refining them: converting them from the grotesque to the subtle, as appropriate. 

Another thing I used to do while I was driving, I would look at people on the street or people in the car next me when stopped at a light.  I would look at their facial characteristics and/or other visible physical characteristics and begin to "put them on" as I sat in the car - exaggerating them in order to really feel them both physically and emotionally.   Then I'd think about the kind of person who would have such physical characteristics; world view, vocal qualities, and so forth.  I'd begin to improvise these things while driving or right there waiting for the light to turn green.  Of course, it was inevitable that from time to time, the person I was emulating would look over at me, see me squinting, contorting my face, and talking to myself (this was before cell phones - now if it looks like someone is talking to himself, he's probably on a cell phone!) and just shake their head - another nut on the road! 

You can also try doing some mental work.  Not everyone relates to mental imaging processes, but if you can relate to it, it can be an extraordinary tool.  Imagine the character, his/her physical characteristics, in as much detail as you can.  After visualizing the character, begin to "put on" the physical characteristics.  Start with the very top of the head and work your way down to the tips of the toes - it's that detailed.  Once you have  essentially sculpted yourself, then add animation:  How does the character breath?  How does the character move?  What are the character's vocal qualities?  There is no right and wrong in this process; there is only exploration and experimentation. 

Like everything else in theatre, it's a creative process.  Dancers and mimes tend to understand physical creativity while the rest of us often have a lot of problems with this aspect of acting. 

There are volumes written and entire courses and advanced courses on the physical aspects of theatre.  When I first got involved with theatre many, many years ago, I studied with one of the great educational innovators in the use of movement and non-verbal communication for the actor:  Nancy King.  She has several books on the subject.  Interestingly, she's more into story telling now than she is into non-verbal communications!  However, her web site is:  www.nancykingstories.com. 

If you need more ideas, let me know.  I've got a lifetime collection of physical theatre techniques!

Knowing your character's daily habits is very helpful in building your exterior.  If he or she lives in a walk-up apartment, the knees will have a bit more wear and tear than usual.  If the character is an executive or sedentary person, you might have a slight swayback from sitting most of the day.  It's the daily routine of a character that shapes his physical standing and carriage.