I've also found that my longer times come from not reading the clues correctly. When I first started solving, I think my average solve time was around 400 seconds. I was happy just to solve the puzzle and didn't care how long it took. When it went below 300 I was thrilled. But I found that trying to speed up resulted in a lot of stupid mistakes. I still make them if I'm not careful.
My solve method is to take care of the "5 people are" clues first and gray them out. Then the positive clues, the negative clues, and the "less than / greater than" clues. I make sure to gray out all the clues I've gone through except for the "less than / greater than" clues so that I can keep revisiting them as squares on the grid get filled in.
I like pcuser's suggestion to read the clues out loud. Either that or slowing down just a bit on the positive/negative clues.
Hope this helps.