Drills are tools and should be used with precision and purpose. Coaches should prescribe and athletes should select and perform drills depending on their individual and evolving needs as a swimmer.
Done correctly, the drills that are suited to you now should not be as useful in 6 weeks because the drill fixed what was incorrect with your form. Consequently, the athlete should change which drills he/she is focusing on.
Figuring out which drills to do is pretty easy after you have your swim analyzed. But if you have not done so, here is a quick listing of what drills to do depending on your needs and level of experience. In the left column is your problem. In the second column is what it looks like. Drills to do in the third column. You will notice that some drills target multiple issues but with different foci when performing the drill.
I have split them into two groups, beginner and intermediate drills. You can usually avoid the more advanced drills by building a strong foundation with the beginning drills. Similarly, the beginning drills will help make the more advanced drills easier to do once you have solved those problems first.
Intermediate Drills (require a bit more experience and focus):
Coach Chris, Tri Swim Coach