All of my clothes go in my closet, whether "in season" or not. I can often find a good use for "summer" pieces in winter, so I just keep everything in there year round. I have a small, Manhattanite closet, but everything still fits in there with plenty of room to spare. My clothing is organized by type (skirts, tees, tops, sweaters, pants, jackets, etc.- suits get split up into their separate categories as I often wear the pieces separately) and within that, sleeve or hem length, and then by color.
All of my shoes, however, do not fit in my closet, so I switch them twice a year when I clean my closet out (once at the beginning of spring, once at the beginning of fall). Shoes wearable for fall and winter are currently lined up neatly on the floor, and spring and summer shoes are in a box under my bed waiting for their turn.
On the top shelf of the closet, I installed cube storage. There are three cubes. Bags go in one cube (yes, it is a bit crowded but it's also a BIG cube, so they do fit). Another contains scarves, and another contains hats and gloves.
On the bottom of the closet, next to my shoes, is a Goodwill bag that i fill on an ongoing basis when I get tired of things or they wear out, etc.
In my dresser drawers, I keep underwear, socks/tights, and PJs. Everything else I prefer to hang up.
In the front closet, downstairs, I keep my most frequently used bags (so they can be there when I switch them out for work each day) and all my outerwear.
I ALWAYS PUT EVERYTHING AWAY. When something comes off my body it goes either to its place as described above, or in the dry cleaning hamper (which my husband empties and takes in once a week) or in the laundry hamper (which I empty and do laundry once a week.) If you let yourself throw clothing on the floor/bed/etc., your organization will quickly disintegrate!
I think that's about all. If you have a manageable amount of clothing, that helps but really it's just coming up with a system and sticking to it.
