Decide how much time and money you want to spend
If you have a lot of money to spend, then you can decorate your room to your heart's content. However, most of the time a decorator will have to work within a budget. If you are on a tight budget, however, you might have to cut some corners. For example: Instead of buying new furniture, you could repaint or refinish your old furniture. Instead of repainting your walls, you could apply vinyl wall decals. This is a popular choice for youth, and for those who cannot paint the walls. also great for those who don't have a lot of time.
Decide on a theme
While you do not absolutely have to have a theme, this will help you decide what furniture to get, and what sorts of colors and patterns to use for things such as walls, bed linens, rugs, and pillows. Start with something that you like, such as a favorite animal, interest, or color.
Consider whether you will like your theme several years from now
If you are planning to stay in your house for a while and are uninterested in redecorating often, will you still like the theme you have now? If you go through different interests often, choose a general theme (such as colors and patterns you like) for the walls, rugs, and furniture. Express your current interests with smaller items you can easily change, such as lampshades, bed linens, or figurines.
Make sure your room is clean
If your room is very messy or cluttered, you might want to clean it first. This will give you a blank slate to work with. It will be easier to move things around and see how they look.
Get rid of unnecessary clutter
Review your room decor. Do you have a theme already in your room, or a mishmash of different themes? Consider getting rid of some items that you no longer use, or that no longer suit your taste or style. You can sell these items online or donate them to a charity center. If you have something that you still like, but that no longer suits the current style of your room, see if you can re-purpose, repaint, or redecorate it.
Consider working with what you already have
If you are on a budget, take a look at your current furniture, and see if you can re-purpose them to fit your new style. A simple wooden bed can easily be made to fit lots of different styles with the right paint job or bed linens. For example: Paint your bed a solid color for a sleek, modern look. Add a colorful quilt and lots of pillows with different patterns for a boho look. For a vintage, country-chic look, you could paint your bed a base color, and then add a second coat of a crackle-effect paint to get that weathered look.
Decorating the Walls and Windows
You can also paint the walls a solid color first, and then paste on a narrow strip of wallpaper going around the room. The strip can be in the center of the wall, or towards the top. If you can't paint the walls or change the wallpaper, tack some fabric to the wall instead. Try to get it as smooth as possible.
Consider having an accent wall
Instead of painting your entire room one color, paint three walls white or off-white, and the fourth wall a darker, contrasting color. Place all of your statement furniture against this wall.