Always when I play SC4 I close my antivirus and every other program I may have running. I then start a program called game booster (http://www.iobit.com/gamebooster.html). It shuts down unnecessary processes that Windows is running all the time and saves me from shutting things down one by one in the Task Manager.
Gamebooster has pretty good default options, but one can also edit these according to ones preferences. I believe that using Gamebooster decreases the risk of CTD.
Otherwise I fully agree with the other above written instrictions.
