You can use the "normal playbook" - by default. This what the CPU is going to run if you don't do anything. There are a couple other "default books for pass and run. You can also turn over your playcalling to the OC/DC...not good if you have my staff. This is different than just the "normal playbook", as it is based on your OC/DC rating and what style you they prefer. What I do, is go an take a look at the team you are up against. Look over their stats and see what they are doing, and what might work against them. You can create a play book for what you want to do, and again....what they are weak in. Sort of works like watching a film on the other team.
I guess, I get too deep with this...but thats just how I coach. I have my playbook set up as to what I want to do on 1st down, 1st and short, 2nd and long, etc...and what plays I want to run in any situation. For instance...UNC did not have any playbooks with a goal line set to use in the redzone. This really hurt my first season...finishing with only 3 wins. I have added the plays and the % I want to run on at the goal line, as well if 4th and very short..and out of FG range, and need a score.