答案：Dear Jack,
I'm glad to get your letter. You asked me about my New Year's plan. Now let me tell you.
First, for self-improvement, I plan to take up a new hobby—painting. Because I think painting can make me calm and help me express my feelings through colors.
Second, regarding health, since I'm not in good health, I decide to do more exercise. For example, I will run for half an hour every morning and play basketball with my friends twice a week.
Third, in terms of study, my English is a bit poor. So I plan to read English newspapers every day and listen to English tapes for half an hour in the evening. I hope to make progress compared with last term.
I believe with these plans, I will have a meaningful new year. What about your New Year's plan?
Yours,
Yang Yang
解析：按照题目要求，包含自我提升、健康、学习三方面要点，层次清晰，使用恰当连接词，字数符合要求，内容合理。