Looking at the room as a whole is overwhelming. Do not look at the big picture, just what is right in front of you as you open the door. Start there, with the things you can touch. No one says you have to tackle this enormous job all at once. In fact, it is better to just spend a 20 to 30 minute session once a day or once every couple of days on the project. These sessions work well because you have energy and do not have to spend hours doing it when it is not in your heart to do so. Short sprits of working on emptying the room will keep your interest in the project and the job will get done because the results will be evidence of your work and give you motivation to continue.
Start right there at the door. Concentrating on everyone elses things. Let's say you come across a box your sister put in your room. Take it to her room or leave it by her hallway for her to deal with. Do the same thing with everyone elses things they stored in your room.
When you get rid of everyone elses things, this is where the real fun begins. You get to reinvent your space by getting three boxes and labeling them:
"Throw Away"= stained or torn clothing; old school papers; anything broken or useless.
"Give Away"= anything you cannot use or wear or do not want
"Put Away"= things you intend to keep and use
Then, when a box is full, do what it says on the box. If it's "throw away", take it out to the trash right away.
If it's "give away" put it in your mom's trunk to be taken to the Good Will or Salvation Army or Catholic Charities or some other place that collects things for the less fortunate
If it's "put away", put it aside with other "put away" items as you will be emptying all of your drawers and closet to put the "put away" things.
Now, you may have to put some stuff in the attic, basement or garage. But, at least take it all out of your room. Your family may be upset that you dumped their things near their door or in their room, but hey, this is your room you are cleaning out of their stuff.
So, how do you keep your room clean? First off, only store what fits in your room IN your room. So, go through your clothing and shoes carefully to realistically keep only what you will be honestly wearing. Buy an over the door shoe holder with clear pockets. This is where you will put your chargers, smaller electronics, your hair brush/comb and any toiletries you may keep in your room, such as hand lotion or hair products and that sort of thing. Those pockets are great for smaller things that usually clutter up your dresser top.
If you have too many things hanging in your closet, you may elect to fold more clothes to put in your drawers or perhaps create a double rod by hanging the top rid higher so you can fit a second rod below to double your handing space. Clothing that is in order, as in folded in your drawers, take up less space. I have a small dresser in my closet that I put my shoes in two drawers and socks in the top drawer. Easy. Convenient.
If your room is small, try to keep the floor space clutter free. You can create tons of storage with wall shelving. Wall shelving is great because it takes up no floor space and it can contain wicker, canvas or metal bins to conceal items you want to store. And, it creates easy access to your stuff, as well.
The key is to have a place for every thing and put everything in it's place. This way, it is easier to keep the place organized so it does not turn into a storage closet again.
While you are at it, you may even want to repaint a wall or rearrange your furniture. This is always good to do every couple of years. I have a summer and wintertime bedroom furniture arrangement. It keeps me loving my room and also forces me to do deep cleaning twice a year.
So, go slow and steady, keep what you love, get rid of things that just are a burden. Remember, the less you keep, the easier it is to keep organized.