Some clothes just make sense to store by season. Accessories, boots, and shoes come to find first, but dress pants, dresses, and sweaters (I have several different weights of sweaters--hey, I live in New England) should store by season. Here's a list of the most obvious types of clothing to store by season, and types you can seasonally store if you need a bit of extra room in your closet.
Accessories really lend themselves to seasonal storage:
Spring and Summer accessories
In the spring/summer, it is light weight scarves, rain boots, and umbrellas.
Rainy day accessories: raincoats, rain boots, umbrellas
Beach Gear: beach bag, beach hat, flip flops
Everyday accessories: lightweight scarves, hats
And then store your...
Fall and Winter accessories
Now it's time to bring out the big guns: your cold weather accessories (which you should store in your home's entryway) should always be easy to access:
Snow day accessories: snow boots, hat, mittens or gloves, heavy scarf, snow suits for little ones
Cold day accessories: coat, boots (maybe your snow boots, maybe a good pair of cold weather walking boots), hat, gloves or mittens, scarfs, etc.
Then do a seasonal sweep and do the opposite in the fall/winter. Here's a guide to How to Store Accessories A-Z.
I divide dresses up by season as well. I keep the wool or sweater dresses in a plastic storage bin during the warm months and swap them out for the summer dresses in October.
In the spring and summer, I store wool pants. They stay in my closet, but I store them in a clear plastic container with silica gel packs. Most other pairs of pants can be worn year-round, but you won't catch me in wool pants in hot, humid July, August or September.
As far as denim, you won't catch me in skinny jeans in the hot months, either.
I know it's fashionable to wear a pair of skinny jeans with boat shoes or a pair of wedge espadrilles, but I only wear skinny jeans tucked into boots in the winter. If you are going to wear ankle-hugging jeans in the summer, make sure they are a little bit cropped.
In the summer, I store turtlenecks. This is despite the fact that I have I have worked in office buildings so cold in the summer due to over-air conditioning, I have contemplated carrying them to work and changing into them in the bathroom - brrr.
I swap drawers in my dresser by season. Long sleeve casual tees and shirts go in the top drawer in the winter and get switched to a lower drawer in the spring and summer.
5. Shoes + Boots
I store my knee-high boots in my closet in the summer because I have such a small shoe collection, however, most people need to store them out of the closet. I stuff mine with paper (you can use newspaper). If you cannot store them standing up, store them laying down in a long plastic bin.
This way you can slide them under the bed or in a storage space. The newspaper will help to whisk any moisture (and, um, odors) from the boots, and to help them hold their shape.
As for activity-specific boots:
I clean and then store my ski boots in my ski boot bag at the bottom of my closet almost year round.
For my snow boots, I wear LL Bean boots so I use them pretty much year-round, except in the deep summer, so I don't store them, but you would store them the same way you stored knee-high boots, with newspaper and in a plastic container.
I store fancy open-toed "summer" shoes, sandals and wedges in, again, clear plastic containers at the top of my closet.
Make sure to clean them first. Flip flops I use year-round. I will wear them in the house in the winter, or keep them in the care in case I get my toes done.
While sneakers and the shoes I wear to work (in an over-air-conditioned office) don't change too much), I so store sandals in the winter and boots in the summer.
Since I live in Connecticut, I have three levels of sweaters: light spring sweaters, wooly fall sweaters, and you-don't-even-want-to-go-outside winter sweaters. I also have two ski sweaters I wear exclusively when I hit the slopes.
I store all of my sweaters in separate stacks in my closet. You could also do this in your dresser, wardrobe or bureau.
The Clothes Organization Series