Add just enough extract to your boil volume to achieve a gravity similar to that of a full boil pre-boil gravity, ~1040-1050ish, then add the rest of the Malt Extract at the 10-15 min mark. This will increase your Hop utilization, and will make your brew slightly lighter in color. Also use carbon filtered water, RO, or Distilled water, as all of the minerals that were in the original water used to make your extract will be present in your wort. That is to say if you are using your tap water, then your mineral/ion content will be that of your tap water plus that of your Malt Extract which can have a significant impact on flavor.
Hope this helps.
Cheers!