When I started my hives, I inspected on a weekly basis. That was mostly for my benefit though because I wanted to know what things looked like, and learn what was normal.
Usually when I would inspect - back then - I liked looking in all the boxes. I would open the top, start by taking out the first two frames nearest me, look at them and set them aside. I could then slide the frames toward me one at a time, looking each over. When I got to the last one, I'd slide them back and replace the other frames.
I'd then take off that box and do it all over in the next box.
It was a long process, and the bees often got tired of me digging around. But for me, I enjoyed seeing all levels so I could learn.
Now I've learned just enough to be able to get an idea what's going on in the hive by just looking at the upper most brood box. I also don't dig in as much, or inspect as often. I just base my inspection times on what it was like the last time checked - were they storing nectar yet? how was the brood? did I put on new foundation last time? If needed, I'll inspect often. Also, if needed, I'll dig into the hive more. In general now though, I just do a quick check to see about honey stores and brood.