Don't overstress the AWA. It's scored seperately and generally considered less important. Other than that, I can only advise you practice - I actually have a few memorized sentences that I think help a lot - but I'm running out the door so I will reply quickly..
I memorized a bunch of phrases like this and tried to use them in my essays. The sound good, they look good, and they are powerful and well structured. I didnt get these phrases from anywhere, I just started making them up and picked the ones that sounded best.
Even though some of my essays were weak, I still got 6.0's on all three attempts.
"The author fails to substantiate the argument that..." (my favourite)
"The passage fails to create a credible argument that..."
"The author does not adequately address alternate explanations..."
"The passage could strengthen it's argument by citing anecdotal or statistical evidence supporting the argument"
"The lack of sufficient statistical evidence leaves the reader unable to reach a well informed conclusion as to the validity of the argument presented."
"The validty of the argument presented in the passage is primarily called into question by ..."
What you dont want to do is write out your points with weak key words like "First,..... Second .... , Thirdly ...." etc
Open your points with a topic sentence in the first paragraph ... for example:
"The passage fails to adequately address the explanation that A caused B, cite convincing and appropriate statistical evidence or support it's argument through anecdotal evidence."
Then passage 1 is about explanation A cause B, paragraph 2 is about lack of statistical evidence, and passage 3 is lack of anecdotal. Paragraph 4 sums its up and re-iterates the point. My final paragraph was always some variation of the following:
"As the passage fails to address the concerns described herein, the reader cannot adequately assess the validity of the argument presented. The author could further strengthen his view by presenting X,Y,Z. Lacking this evidence, the author fails to adequately substantiate his claim."
I have some tips for the other essay too... I'll write more here later. PM me if i forget.