I've been working at my combat rank off/on for the last year or so. Exploration and trading came with little effort through ordinary gameplay, but combat is a different beast altogether. I spent several months parked in Subra, a good pirate massacre stacking system. I figured I may as well try to make some credits at the same time; it would be doubly beneficial and help tone down the boredom. I'd spend a few days grinding out a batch of massacre missions, then get bored and venture off somewhere else for a week (or several).
After the recent tritium CG gold rush, credits are no longer a concern for myself along with half of the current player base, so I decided to try and figure out if there are any quicker ways to grind out combat rank since I no longer really need the missions. The most popular but least likely solution seems to be seeking out Anarchy systems in Outbreak, although they occur very rarely, and are an unreliable source to grind simply because you can go weeks or months without another popping up.
So, I figured I'd just find a high population system currently at war, and farm some High CZ's. I'd gotten bored of pirate hunting, anyway. The long downtime traveling between signal sources or waiting between fresh targets in Hazardous RES's was exceptionally boring by this point, and the last time I hit up a CZ was for a community goal several months ago. I found one close to where I was, jumped my FC in, and started farming the nearest High CZ.
I gained 4% in about an hour, which is more progress than I've made in the past month or two. Given, I haven't been particularly dedicated recently, but that's a good amount of progress for such a short time. High CZ's are a nonstop stream of high-ranked NPC's.
Anyway, just sharing my experience. If you're looking at the combat rank grind and you've got a ship capable of soloing High CZ's, consider going that route rather than chasing pirates around a random system. Might save a little bit of your sanity for other activities afterward.
Source: https://www.reddit.com/r/EliteDangerous/comments/vc5ko3/the_long_painful_grind_from_deadly_to_elite/