I have a number of drills to help students with this. The funny part is that the drills are incorporated in the children's class and show up in their first test. It is easier to help reshape a child's response set because of less history on the response set. For the children, they learn tenkan and irimi movements into shomen strikes and mune tsuki with a bokken (requirements on their first and second tests).
With adults, I like the Systema training philosophy of training movement to be relaxed and centered while slowly ramping up the intensity and speed of an attack. As soon as the initial response set fails, it is important to back down the intensity. This is a function of "rewiring" how the body reacts to situations. These drills focus on connecting to the center of the attacker so that the initial movement and/or contact point results in either kazushi, or the locking-up of the attacker's body, while retaining a relaxed, positive and calm center in yourself. Many people just go through techniques with little thought to the very first point of connection (before contact) through the initial contact point. Frequently, people start their training after contact has been made. I would be very remiss to not point out that this emphasis in how to train was directly learned from my good friend and a teacher to me, George Ledyard Sensei.
Last week, I was working with the adults on entering into attacks from a Jo, rather than flinching or withdrawing (both of which have bad outcomes).
I frequently emphasize to my students that if their initial positions and responses are not good, then all of the techniques in the world that they may know will not be of use to them.
Funny enough, I was going to give this blog another title, which I also use in class. That is "killing them with kindness." That sounds much too violent for us peace-loving Aikidoka