Answer:
English: I do well on short assignments. I need to do <u>better</u> this year than last year on long assignments.
Math: I should work <u>more</u> carefully on my homework than I did last year.
Science: I work the <u>fastest</u> in the labs. I clean up the <u>best</u> of all. I need to improve this.
Explanation:
you will find the changes underlined above^^
fixed the first sentence that needs improvement by adding the word <em>better</em>
added the word <em>more </em>in the next sentence that needed fixing
changed <em>faster</em> to <em>fastest </em>on the fourth
and finally, changed <em>better </em>into <em>best</em>