Speaking from both a producer and a recipient of these reports:
The most important things for me are:
- Revenue
- Conversions
- Traffic
In that order.
For any SEO report, I would be expecting to see, above all else, how much organic visitors (or people who have visited from organic search in some part of their user journey) have generated in terms of revenue. Some companies model this entirely within Google Analytics, others may have a CRM that stores the customer financial data that you'll need to sync up with analytics. But basically, show them **how much money **organic search has made them last month.
After that, I'd want to see how many organic search visitors converted on the site (bought something, signed up etc). It's worth reporting this separately from revenue, as you can get an idea of which conversions are more "valuable" to you. Show them how many conversions organic search has given them.
Next, look at traffic. This is important to report as you need to show them how much organic search is contributing to their overall traffic, and hopefully show them it is increasing. It can also help you identify other issues - for example, if traffic increases but revenue or conversions do not, is there a problem with the quality of the traffic or, more likely, a problem with the website's user journey or design? Remember, organic search is inbound marketing, and so searchers are actively looking for the thing that drives them to your web page. If you can get organic traffic but can't get it to convert, it is usually a problem with your website's design or UX. Show them how many visitors organic search has given them.
Anything else, to a company receiving an update on how SEO is progressing, is just fluff. My clients don't need to see things like error rate, crawl indexing, canonical reporting - even rankings (a sub-KPI of traffic, but ultimately not what the client is interested in). For a top level report - something that says what has our money got us - I stick with these three principles. If I'm producing a technical audit on the website, then of course you want to give more detail, but for a general monthly report it's overkill.
There are caveats to all of this (such as breaking down branded vs non-branded organic traffic), but this should be the starting point.
Hope this helps.