Definitions:
Skill- a particular ability
Technique- a way of carrying out a particular task
Tactic- an action or strategy carefully planned to achieve a specific end
Tip:
The training industry can sometimes be very confusing. An instructor will put together a curriculum with the skills they deem to be indispensable, the pass it along to their students. The problem is that rarely are these skills ever developed into interlocking techniques or tactics.
Skill is the "what are we doing" of using the firearm. It is working a trigger without disturbing the sights, performing a reload, or clearing a malfunction. This is absolutely necessary to master, as you may not have the extra brainpower to manipulate the firearm AND solve the other problems of the attack (Is this person a deadly threat, how do I get to cover, etc.).
Techniques are the "how do we do this task" of firearms training. A techniques is a set of manipulations (skills) that get combined to make the skills more effective/efficient. Choosing the most effective and efficient technique is all about the tools and abilities of the individual.
Tactics are the "why and when" to use defensive tools. Once we have our skills mastered, and our techniques chosen, we need to apply them to the world. This takes the largest portion of our mental ability. The application of skills and techniques to the world requires that you are able to decide when and why those techniques are appropriate. This should start before you ever get into a defensive situation. pre-plan your responses in training. Then you put your plan into action.
Understanding the level your skills and techniques should be at is the first step in developing the right mindset, and critical to ensuring that the tactics you choose are appropriate to a defensive situation. Make sure all bases are covered in your training.