OK, the general point:
Almost every form of Cmdr progress can be achieved via visiting specific persistent Points of Interest. Some contain unique things, others things within a category yet similar. These permit the player to force-refresh something of value, generating an infinite stream of xp / materials.
The most widely-known example is the unique persistent POI known as "Dav's Hope", which permits the player to force-refresh g1 to g4 Engineering materials of the manufactured variety.
However, there are a number of others, which permit the player to force-refresh elemental materials, wakes (for scanning), data points (for scanning) and yes, ships to be killed for combat rank, amongst other things.
So, basically, from a perspective of pure min/maxed time, pretty much everytime someone goes to a non-unique location ... every time they drive on a planet for elements, or go to a Nav Beacon for rank ... they may be enjoying their gameplay personally but from a time-only perspective they're going sub-optimal.
Frontier have actually been very generous with the Easter Eggs. I repeat that this will really come into its own with the Materials Trader, hence my forthcoming guide.
However, dealing specifically with combat rank, I hope it's clear from the above that, although CNB and Haz Res are pretty good, optimal progress will be found via visiting the Developer's POI's and force-refreshing the NPC's that spawn there. This is because:
(a) the spawn of the desired NPC(s) will usually be quicker;
(b) the ships spawn location will usually be closer to the player;
(c) the desired NPC's will be more predictable, i.e. either identical or near-identical, meaning their rank and characteristics can be tailored to the player's needs.
So, at lower ranks, you would do well visiting for example the Type-9 trader locations that spawn (not permanently) when certain conditions are met. For permanent spawn, tourist locations and their attendant Belugas. Both are good sources of both rank and materials, most obviously as you're already aware in anarchy or low-sec systems.
However, as you're already Master rank you'll soon need to go to places where you can force-refresh higher ranked targets. Ideally that can't really fight back. Ideally 100% consistently.
Before doing the second spoiler I'm going to repeat the basics, therefore. To obtain almost any benefit in Elite Dangerous in the most time-effective (even if, otherwise, arid) way, you need to:
(a) identify a POI that spawns what you want;
(b) ideally a permanent, not state-specific, POI;
(c) even better a unique 'Easter Egg' POI.
I don't want to sound defensive but I'm going to forestall any arguments about 'exploits'. I am talking about POI's provided specifically by the Developer, which we as paying customers are entitled to visit as many times as we personally choose to and do whatever we like to the hapless NPC's when we get there, as many times as we want.
In the particular example I'm going to give you next, the Developer has actually coded in occasional humorous NPC dialogue to cater for the (rather obvious) possibility of being shot at and, indeed, blown up.
OK, on to the actual answer. I warn you that like most such things, kind of like stage magic tricks, it's a bit of an anti-climax when you learn it. So, again, open the second spoiler only if you want maximum time-efficiency.
