Here are some sources for suggestions on how to improve your writing; in my experience, one's writing can only be improved with reflective practice: writing, thinking about it and getting feedback from others and revising and re-writing. These sources give tips on how to do that:

1. An online article by Jim Pryor called "Guidelines on Writing a Philosophy Paper":
http://www.jimpryor.net/teaching/guidelines/writing.html

2. Some chapters on writing from A Rulebook for Arguments;
http://www.amazon.com/A-Rulebook-Arguments-Anthony-Weston/dp/0872209547/ref=sr_1_1?s=books&ie=UTF8&qid=1332425273&sr=1-1

VII. Composing an Argumentative Essay
A. Exploring the Issue
VIII. Composing an Argumentative Essay
B. Main Points of the Essay
IX. Composing an Argumentative Essay
C. Writing
&
I. Composing a Short Argument: Some General Rules

3. Strunk and White's The Elements of Style, the section III. ELEMENTARY PRINCIPLES OF COMPOSITION:
http://www.bartleby.com/141/strunk5.html

4. Some tips from me:

• The most common comments I write on papers are these: (1) What do you mean? and (2) Why think that? The first is in response to unclear claims: write clearly. The second is in response to claims that need defense: give reasons.
• Write in short sentences: if any longer sentence can be broken into two or more sentences, do it because it's easier to read then.
• Each paragraph should deal with one, and only one, topic. You should be able to say, "This paragraph is about this: _____."
• Omit all needless words and needless discussion. Your reader's time is valuable so don't waste it.
• Make sure everything is clear. Use simple words: no need for anything nebulous.
• Your papers should have a short introduction, culminating in a thesis, a main point, the point that your paper is supposed to defend. The most direct way of presenting this sort of thesis is this: "I will argue that _(short sentence here: 'all abortions are wrong', 'Dr. Doopy's argument against euthenasia is unsound,' etc.___."
• Your introductory paragraph, or a paragraph immediately after it, should give the reader an overview of what you will be doing in the paper. It should briefly explain the overall structure (e.g., "First I will ___ and then I will ____. Finally I will ______.")
• Omit anything totally obvious and uninformative (e.g., "This issue has been debated for hundreds of years."). Everyone already knows this, so don't waste time telling us what we already know.
• Don't write, "Well, _____." No "well's".
• Don't say, "'Mr. Bubbles feels that this is wrong." Say, he believes, or thinks, or (if he does) argues. His views are probably not his "feelings" or his emotional reactions.
• Also, no ' . . . ' unless you are shortening a quote. No "trailing off" in hopes that the reader will think what you are hoping they will think.
• Don't ask rhetorical questions. Make statements, don't ask questions. Your reader might answer your questions for you in ways you'd like. But if you do ask questions, make sure there is a question mark.
  
• It's OK to use "I". People use "I" to communicate clearly, so use it.
• "Arguments" are not people's conclusions. They are the conclusions and the reasons they give in favor of those conclusions.
• If I ask you to raise objections to a theory, argument, claim, or whatever, it's fine to raise objections that are discussed in our readings. What's not good, however, is to raise an objection that is discussed in the readings but the author responds to the objection and shows that it's not a good objection. If you raise this same objection, but do not discuss the author's response (and respond to that response), this suggests that you didn't do the reading very closely.
• If an author states a conclusion (or a main point) and gives reasons for it, then that author has given an argument. If an author has given an argument, do not say that the author has not given an argument: you might not have found the argument (yet), but the argument is still there! Keep looking!
• Keep focused and don't argue for more than you can give reasons for.
• You have succeeded in writing a paper if you can give that paper to a smart and critical someone who is not familiar with your topic and this person will understand the views and arguments you are discussing, as well as whatever criticisms you raise. You can do an empirical test to determine whether you are writing well, and it's basically just to see if others understand your writing! If not, you need to keep working at it.
• Finally, good writing, like many things, takes a lot of time. If you don't take the time to work at it, you probably won't do very well and you probably won't improve. I recommend writing something about double the length needed and then editing down and re-organizing and re-writing to remove the needless words, irrelevant distractions, and -- most importantly -- improve your statement of whatever argument you are trying to develop.

On Writing Well, 30th Anniversary Edition: The Classic Guide to Writing Nonfiction [Paperback]

William Zinsser

http://www.amazon.com/Writing-Well-30th-Anniversary-Nonfiction/dp/0060891548

 http://www.amazon.com/How-Write-Reflections-Richard-Rhodes/dp/0688149480/ref=sr_1_1?s=books&ie=UTF8&qid=1332200135&sr=1-1


On Writing Well by Zinsser, How to Write by Richard Rhodes, On Writing by Stephen King.
http://www.amazon.com/On-Writing-Anniversary-Edition-Memoir/dp/1439156816/ref=sr_1_1?s=books&ie=UTF8&qid=1332200225&sr=1-1