To learn how to write better I suggest reading guides about basic grammar and writing. You might find them helpful to refresh your memory about concepts you were supposed to be taught in grade school and high school.
Purdue has an excellent online resource: http://owl.english.purdue.edu/owl/
PS: To all, there's easily a resistance or even antipathy towards grammar, punctuation, spelling, etc. This is unfortunate, as everyone can improve. (Yes, I check the dictionary too many times to count.) Graduate and especially doctoral students spend much of their time proofing and re-proofing their work, and woe be unto the graduate student who repeats a basic error. (Actually, not always. They will, however, find it hard to get stellar recommendations and inside job tips.) In law school, this is confined mostly to a process that's rather important in a different sense than learning: the application process. Know that faculty members sitting on admissions committees--and everyone else in admissions--cares about this, rather a lot.