A double tap is two aimed shots.
If you want to get better, compete. Join your local USPSA or IDPA league. Get squadded with shooters who are better shooters than you are.
The pressure of shooting in front of the peanut gallery will, at first, make you want to rush. You'll make mistakes, drop shots, etc. Eventually, you'll reach the frustration point and begin to work hard to see where each shot goes, quickly.
From my experience, people put way too much emphasis on how quickly they shoot, and don't bother to put emphasis on where those quick shots end up. Walking along your targets as they're scored with your squad as the RO calls out "one Alpha, one miss, one Charlie, one miss" makes the lesson sink in. Learn to see your front sight all the time- up and down in recoil. Focus on that.
BTW, first shot aimed, second shot unaimed is "The Hammer".