I spent a ton of time at the beginning analyzing Neko's spreadsheet. DH called it "looking at the tea leaves". Identifying patterns is key. And it's not just a single cycle, but a pattern over several of them. On Lantus, Neko had a particular three cycle pattern where the 3rd was a dive to lows. Libby calls it "waves of action". After a while I started playing "guess the BG" when I did a test, after looking at her spreadsheet first. When I switched to Levemir, the most frustrating part was learning patterns all over again. The best part was that a lot of days I could get away with 5-6 tests. Learning when onset, nadir and duration are help you be strategic about when to test.
And listen to and watch Zeke. In the beginning, Neko was playful in the low 300's.

Later it became low blues. Does Zeke start giving you hints about food when he gets into greens? Neko used to head for the kitchen when her numbers were getting lower. If she lay down in front of the fridge, I got out the test kit.