I test first thing (fasting), before meals and 2 hours after, so 7 times a day, sometimes more. I record all the readings and everything I eat. This gives me a picture over the months of what spikes me and what doesn't. Then hopefully my annual HbA1C result will be a bit lower.
These days I stop testing for up to 3 weeks and then do another week, 7 times a day, 7 days, and add it to the record. I now experiment more with one-off trials of, for example, low-carb bread.
Random tests tell me nothing really.