I just have got the MA arts and design program offer from leeds, there are some experience may work for you.
Basically you just need to do some project around specific themes such as social problems, environment issues or some problem or interest things about your life. you need to share why do you want to do it, how do you survey this theme and what kind of experiment about graphs you done. finally, you can show some pictures or paints, books or whatever you create.
the most important thing about your portfolio is that you need to show your special thinking and opinion clearly and I suggest you to translate them to the graphs especially for applying this program.
I wish you can gain the admission, good luck ; )