Use Your Non Dominant Hand
Wanting to paint more loosely? Try painting with your non dominant hand for a day. This way you won't stay in the lines and you will have more expression to your line.
Here are some things to try:
Things in your purse
Compose with pencil one of your favorite items
Draw with your dominant hand
Find your color scheme
When ready to paint, paint with non dominant hand and a large brush you don't normally work with.
Do several paintings this way.