Reporting is very important as it gives you and your client the opportunity to create an effective snapshot of the activity of the AdWords account.
Every report should contain elements that are easy to skip through but still give a great understanding of what's going on advertising wise.
Your report should include the following macro areas:
Not all of your clients are AdWords gurus. That's why they hired you. It is fundamental to include a list of AdWords related terms you will use in your account. Also, make sure to explain the most common relationships among parameters (e.g. if the number of clicks increases and the impressions stay steady, the CTR is going to increase as well. You can include this example when you explain the term CTR)
2. Account Snapshot
What are the most important metrics in your account? Create a standardized table or graphs to help you organize the data. You will learn a lot about your account in minutes!
3. Keywords Analysis
Identify your top performing and least performing keywords in your account and retrieve all data associated to them. Analyze the data and ask yourself what you can do to improve the current situation.
There are different kinds of keyword analysis techniques out there. Find out the one that best fits your advertising strategy and scale it to all of your accounts.
4. Website Analysis
How is your website performing? Is your average time on site good? Do you have a high or low bounce rate? How is the time on site of the paid traffic compared to other advertising means?
This section of the report should be able to answer all of these questions!
5. Data Interpretation
This section of the report should be used to add value to all the numbers you mentioned so far. What is good or bad news? How can you improve what's going good and reverse what's going bad? What are your next moves in the account optimization?
This is the most important part of the report. Make it clear, easy to read, and to the point.
Creating a report is useful also if you manage your own account as it will let you focus on aspects you would not consider otherwise.