Simon K & 1071 S have got it right .
My suggestion to you would be to obtain some Mini manuals and do some reading first , you're a young
fella , you'll pick it up quick ,

,even check out YouTube to get an idea of how things work , some mechanical knowledge , you'll start to get an understanding of how these cars tick , ie; tuning , suspension , modifications , so forth , also do some searching on here , there has been plenty of questions on the same subject .
One major thing i would say to you is , DON'T , rush in and spend heaps of unecessary money on mods that you don't need . Start saving some money each week, ( give yourself a plan & budget ) and do some research in the mean time , and when you start to work out what you want , you can then make some plans to make it happen .
There are plenty of people on here that can lead you in the right direction , so don't be afraid to ask , no matter how small you think it is .
Just to give you an idea of dollars that you could spend , anywhere from $2 K - $ 20 K + , to get some
performance increases is not out of the question.