Well my first reccommendation would be to go to the clearance fabric section and pick up a few yards.
When I first started, I bought expensive fabric and trim that I inevitably ruined, lol -- so definitely go w/cheap or even plain fabric to start.
I'd also start with a basic cotton fabric, no stretch (to learn on).
You could try a pattern, but if you're very new to sewing they may be confusing so try to find ones for beginners or even buy a book that can help you w/the sewing terms on the pattern.
Most of all, have fun and practice w/your machine before you attempt to construct a garment so that you have all the basics mastered
Good luck and happy sewing!!