This page offers brief info to help with writing.
You can also consult, and use (e.g. get a tutor), at the Centre for Applied English Studies (CAES) at HKU. CAES at HKU
The number one all-time tip for turning in better essays and scoring higher grades on them is to leave enough time aside, after the "final" draft, for a thorough proof-reading and editing. Feel free to write on and mark-up the final copy of the paper, as it shows me that you've tried to proof and copy-edit a bit. Big brownie points for that right there.
The number two tip -- it is actually more important but harder to do -- is to get your draft done early enough to run it by someone for comments and reactions. That person can be me, your tutor, a friend, a classmate, and -- again -- someone from the CAES linked above.
1. http://owl.english.purdue.edu/ This is the Online Writing Center at Purdue University. Excellent resource for all types of writing and better than anything I have seen elsewhere.
2. http://writingcenter.unc.edu/resources/handouts-demos/writing-the-paper/argument A short but sweet explanation on how to write argumentatively in an academic way.
3. Find and read this book: They Say, I Say: The Moves That Matter in Academic Writing. By G. Graff and C. Birkenstein. Parts of this are here: http://www.csub.edu/eap-riap/theysay.pdf This is a very helpful and specific little text on purposeful writing.
4. Use the MLA format for citing things: http://www.citationmachine.net/mla/cite-a-website