答案：One possible version:
I was a little fat last year. So my most important New Year's resolution was to lose weight. I kept it by running and eating less meat.（点明去年最重要的新年决心是减肥，使用by doing sth介绍了实现这个决心的方法）Now I make it.
The new year is coming. I have three resolutions. Firstly, I'm going to keep on exercising and eating less junk food to stay healthy. The second resolution has to do with my studies. I want to get better grades, so I'm going to study harder next year. My last resolution is about my hobby. I want to be a basketball player when I grow up, so I plan to join the basketball club to play basketball after school at least three times a week.（使用firstly, the second resolution与my last resolution介绍新一年的三个决心，条理清晰；动词短语keep on doing sth, want to do sth, plan to do sth以及状语从句when I grow up的使用，显示了作者良好的语言表达能力）
Although it's difficult to keep these three resolutions, I'm going to try my best.（although引导的让步状语从句是高分句型）I believe where there is a will, there is a way.（结尾使用谚语，增强了文章的感染力）