I took a flower arranging class in college just for fun. It was one of my favorite classes!
So basically, you just need to figure out what you flowers you want, choose a filler for here and there and place it in a vase... voila! Amateur flower arranger! Also, you want to work in 3's. 3 roses, 3 tulips or 3 of the same color, or 3 different colors. It just goes together better that way. Varying heights in flower and filler are more pleasing to the eye, unless you are going for the round look. Then don't do it. :) My favorite are the vertical arrangements which is pictured below.
All the flowers and filler and vase I bought at Michaels
I think that flowers are an easy, cheap, and GREAT way to but a little bit of spring into your home.