Additional Official Guidance
You asked about any official guidance that you've missed. I am not aware of additional specific guidance about how to select within the random treasure tables.
However, there is broader guidance that's worth considering.
It's Your World
Chapter 1 of the DMG, It's Your World, talks about "the default assumptions" in the PHB, the MM, and the DMG, and how you might change those assumptions.
Chapter 1 of XGE under, This Is Your Life says:
Even though these pages are full of tables and die rolls, they don’t make up a rules system — in fact, the opposite is true. You can use as much or as little of this material as you desire, and you can make decisions in any order you want.
True, those sections of the DMG and XGE are not specifically talking about treasure tables, but the general guidance might be relevant.
You Can Decide
You asked "what techniques for assigning these sorts of items have you found to work well in your own game?"
Make the Treasure Fit the Story
I find it is often useful to make the treasure fit the story.
The random treasure tables are nice, perhaps particularly for a large horde, but I've found it often makes sense to just decide what the treasure is, and use the treasure tables as idea generators and general guidance.
While it's reasonable to consider what would be interesting to the PCs, I am generally more focused on considering what treasure is reasonable to find at that particular time and place, and let the PCs worry about who gets which what. Heck, eventually (like 2 seconds after they count it up) they'll want to know if they can use their small hill of gold to buy whatever magic item it is that they want. The quest to buy that +1 heavy crossbow can be an adventure all it's own, and may or may not be successful.
If the party is confronted by bandits, the bandits would be using any magic items that they have, unless they don't know what the items are or how to use them. So maybe the bandit leader has a +1 sword. When the PCs say, "we search the bodies", (as they seem to say so often), you don't even have to say, "you find a +1 sword", perhaps you give a hint and say, "the bandit leader's sword looks particularly well-crafted". Similarly, other treasure the bandits are carrying might be simple things like a healing potion, although the bandits should actually use it if they get a chance.
Ogres, on the other hand, are, according to their description, avaricious and stupid, and live by raiding. As CR 2 monsters, they're unlikely to have accidentally acquired any really powerful magic items, but whatever they've acquired, they might have just left lying around, being too stupid to use or sell it. Since the description says they particularly have a taste for dwarves, halflings, and elves, it is easy to imagine that past victims included a party of dwarves, for instance, and +1 chain and a +1 hammer or battleax might be reasonable things to find in a trash pile in an ogre lair.
An Ancient Temple
As a third example, perhaps they party is investigating an old abandoned temple, lying in ruins for a thousand years, with generations of creatures lairing in it. As the PCs search it, they might find loot reasonable to associate with whatever monsters they defeat, or even previous monsters that have laired there over the centuries, but should they find the chief priest's inner sanctum behind a secret door, they find a room untouched for a millenia, and in it they find items befitting the priest, perhaps vestments that fall apart at a touch, or scrolls of cleric spells, or even a fairly significant item like a Rod of Security or a Scarab of Protection. Or maybe some priestess queen was buried beneath the temple and and items of fearful power were buried with her.
So, what's worked for me is to use the treasure and magic items sections of the books as general guidance, and to make the treasure fit the story.