How can I break in my Shetland Pony?

I want to brake my Shetland into riding. I don't want to use a saddle or bridle because I will be riding her in only a halter and rope. She basically will just be for playing about on. She's more of a pet than a riding pony. So if you could tell me all the ways of breaking my Shetland and what I should do and I would be most happy. Im 13 and weigh 42kg, which is light in comparison to my height and age, I have also been riding all my life! Please no abusive or sarcastic answers please. Thank you!