good suggestions from Mo! i'd start with gathering together the clothes that you tend to wear now, then shop your closet to see what else you can toss in there - do you have a pair of jeans that could work with your ankle boots, nicer tee and belted cardi, for instance? this will help you focus your 'non-closet shopping'.
it's also a good idea to think about how you're wearing your looks during your outings - are you always so cold that no one ever sees that cute blouse underneath your sweater? if that's the case, go for festive jackets, cardis, scarves that you can wear over a long sleeved tee. if you do a ton of walking (like i do), focus on foot wear that love your feet. and so on.
a couple of ideas that are helpful for me in making capsules - try to find pieces that can work with the more casual pieces in your wardrobe. Throwing on a tee, jeans and heels with Mo's tuxedo jacket would be a fun look for many restaurants or at a comedy club. If there is a basic item (pants, skirt, jacket, blouse) that you love and it really works for you, you can 'stretch' it by buying it in two colors (if available). a lighter version and a darker version of the same garment tend to look pretty different, but you can interchange them in the same outfit nine times out of ten for two different looks. white and black, dark denim and khaki, olive drab and tangerine....it depends on your palette.
i find people focus on your face, so i'd start with 2-3 bottoms (hopefully ones that you can wear with different shoes to change them up a bit) and then focus on pieces that will change up your above the waist look. Again, Mo's advice on choosing a palette is very wise - the more you can intermix your 'above the waist' pieces, the more possibility for variety. don't neglect scarves, statement necklaces, earrings either - and there are some great pieces on sale a thrift stores, etc.
what a fun project! and a good idea! steph