This site has a plethora of workouts designed for everyone from the Beginner to the Advanced Swimmer. Anywhere form 600 yards to 3400 yards. Work your way up at your own pace.
A workout should have a purpose and methods to achieve that purpose.
Here is an example of how to layout your workout to give you a more complete session in the pool.
Here is a little article on Freestyle Breathing.
Just the basics that everyone should work on.
Don't say "I don't know any drills".
Here you go, dig in.