How to show appreciation to parents more?

My parents came from nothing, and have built everything up from the bottom, and although we are not rich nor poor, I feel like i take too much granted for them. I have a little sister, but sometimes I get mad at the fact I'm always blamed for everything she does wrong. Additionally, if I ever ask for something, its always a problem. I do appreciate the fact that my parents make things for me and give me things, especially when it comes to the few pets I have and the things my dad has built for me to make them happy with. I'm 15 and I am getting a job soon to return some of the copious amounts of money they spend on me but also saving up for my own horse so its not given to me by them yet again. I do feel bad that I'm lazy and sit on the computer instead of picking up a vacuum and I really do want to be nicer and help them out more. My family in general is great, but Ive always been the youngest amongst everyone, until my sister. I just hate having to hear "oh when you were a kid you were so terrible" or "wow youve changed, youve become so much nicer" - those things urk me and I just want to be a nicer person. I feel like I'm mean because if I wasn't, then nobody would notice me in my family.. I also know that I AM spoiled and I get things that most people envy because their parents wont let them have, but I still ask for something new all the time and I annoy my parents when I dont mean to.