The above posters have already covered most of this, but I want to emphasize. Clutter. Is. Bad.
My mom's house is very cluttered and I can tell that it distracts her all the time. I didn't realize how distracted I was by it until I moved out (I'm in a college dorm now and in control of my own space--very empowering!). So, only keep what is important and you will have a clearer mind. (For me, I don't even have a need to keep "sentimental" objects because I can remember good times without looking at a thing.)
That's my 2 cents.
~Jm4362