I have tried a few instructors over the years and before committing to a series of lessons, I would try a couple of instructors to see who best fits your game and learning style. With that said, one 30 minute lesson can go a long way when it comes to addressing the basics - set-up, grip & alignment.
For example, during my first lesson, my instructor was able to identify a couple of issues with my grip and alignment that made a world of difference. After working on those at the range & on the course, I returned a month later to start a series of lessons, 6 for $200 which were spread over 10-12 weeks.
As you begin to correct certain areas of your game, you will see other flaws that may have gone un-noticed. I fixed my slice and realized my short game was horrible . . . then I could not find my putting speed etc. As another member said - know what you want to work on, otherwise the instructor may be continuing the same thought progress as the previous student. Describe the problem and what you hope to achieve. If you get nothing from the lesson, at least part of the blame lays on the student.
Good luck.