I'll give you my advice: if you have a basement, start there. (If you don't have a basement, start with the attic.) Take three empty bins and sort through a small area, putting "give away/throw away" stuff in one bin, "keep (hidden)" stuff in the second bin, and things you'd like to display in the last bin. Once all three bins are full you will have enough room to move around. Immediately throw away or give away the stuff in the first bin. DO NOT keep it. Once it's gone, repeat the process, (and don't stall, or this will become part of the clutter problem, not the organizing solution). Start stacking the sorted bins and labelling them clearly. You should create a shelving system in the basement for these bins. Many people even designate an entire area as their holiday decoration area, so they're not digging through everything trying to find what they need.
How do you know what to keep and what to toss? If it isn't aesthetically beautiful, very useful, or doesn't have a deep sentimental value, you don't need it.
My basement (above) is not the greatest, nor is it finished, but thanks to the shelves and bins/boxes, it is clutter-free and has a lot of room left over for things I might need to put down there in the future.
Once the basement is sorted and there is no clutter left, you can move upstairs. The reason why it is important to start with the basement is a) because the things you've stored down there are often overlooked or unnecessary (you might be buying something you already have or keeping something you don't need that is eating up space), and b) once the basement is clean you will have enough space to store things that are upstairs and shouldn't be there, such as extras and holiday/seasonal items. Not everyone has space for storage upstairs, and we resort to tossing stuff in the basement and forgetting about it. It is much easier on us when everything is labeled and organized. Only you will know what can be stored in the basement, but at the very least it will be clean after you go through it and you will know exactly what's down there.
Since I have no room in the kitchen, all of my extra food and extra stuff is in the basement in one concentrated area so I always know what I have.
Repeat the process upstairs. You can find extra room in your closet if you put your seasonal clothes in waterproof bins in the basement, and likewise for coats and blankets. There might be a ton of stuff that can go into hiding - things like a relative's wedding dress, baby items you might need in the future, etc. For coats and dresses, make a closet in the basement. Pop-up closets are readily available at places like Bed, Bath and Beyond. The same goes for shoe storage. If you "think seasonally," you will have a lot more space year-round, alternating winter boots in a bin for summer sandals, etc.
Our shoe and coat storage is in the same place, half way down the stairs to the basement.
Remember the "give away/throw away" bin. Go through every room with this bin, and do this once a year. Once you've gotten rid of everything you don't want anymore you will have a lot more space. Next, tackle all those papers lying around. Every important document should be filed in a safe place, not just shoved in a drawer. Should you need that old surgery bill and the new electric bill at the same time, they'll both be in the same place. File cabinets can be stored in the basement as well, but otherwise, there should be a clear "office space" in your house. Try converting a bedroom closet into an office. Also, with new technology we are able to file papers electronically using scanners. This is a real space saver.
Everything else should be a breeze after that. Put pens in old mason jars, spare note paper in a shoe box, paper plates and plastic cups in a picnic basket, and magazines in a magazine holder. Everything should have a designated "put-away" spot.