Have fun with the different colours but tie in the art with pops of colour in your furnishings such as a cushion, a throw rug etc. I love a throw over the bedspread that complements the colours in your art.
If you have a big bare wall, go with a statement piece - it has a stunning effect. Be sure to have the centre of the art piece at eye height. You want impact, you have to have it at the right height to feel the WOW.
If you want the room to feel fabulous each time you enter - select pieces you love. It is an extension of you and you are surrounded by it every day so make sure it makes YOU feel great and YOU love what you are looking at. The Little Rae Prints I hang in my children's rooms makes us feel like we are enveloped in warmth and magic when we enter.