Use knowledge about how people remember things to your advantage. There's a number of websites, books, etc. out there talking about how people remember and providing tips and tricks for memorizing. As a writer, you can incorporate lessons from these aides memoire into your writing.
Repetition People remember things better when they're encountered multiple times. Readers will be familiar with your main characters' names because they'll happen on practically every page. That minor government official mentioned once, 200 pages back? Probably not. The same minor government official, but who now has been popping up repeatedly in several chapters? Much better chance of being recognized.
Method of loci People's memories are highly contextual. You might recognize a barista on sight when at your local coffee shop, but completely fail to recognize them when you're at the DMV. The coffee shop environment primes you to remember things related to the coffee shop. Likewise in writing, it's easier to remember a priest if they're re-introduced in the context of a church, rather than in a bakery. As a writer, be aware of the contexts your characters appear in, and be more conscientious about re-introducing characters who re-occur outside of their standard context.
General vs. specific It's much easier to remember the general outline of things, rather than specific details. So people might remember that someone is a Lannister, but forget exactly how they're related to Tyrion. When you're writing things that may be forgotten, don't overload the reader with "useless" details, and make sure that the "general outline" of the character you present is the salient feature which will become important later.
Related to this, remember that the main interface you'll present to readers is the name of the item. All too often writers will use names that are very similar to each other (e.g. Ori/Dori/Nori, Bifur/Bofur/Bombur). If all readers remember is the general outline of the name, the exact details (i?/o?) may be glossed over. This gets worse for polysyllabic names. Only the most astute reader will remember - or possibly even notice - the distinction between Amaphidalia and Amothifalia. Using unique and distinguishable names helps to keep people from confusing things.
That said, sometimes similarity of names is helpful. For example, if you're attempting to invoke the trope of "practically indistinguishable siblings" (e.g. Fili/Kili), or if the relationship between objects is the most important trait (e.g. the Amaphae people are ruled by the Amaphidalia from the capital city of Amaphidon), using similar names may be warranted. If using related names to show a relationship, be sure to introduce them in close proximity to each other, so readers are clear on the relationship and are alert to the distinction.
Connections One very important point about memory is that memory is less about facts and more about the connections between facts. The richer you can make the interaction of your characters with the "interesting" parts of your world (while simultaneously avoiding unnecessary details), the better your readers will remember them. That named-but-faceless guard isn't going to stand out, but one with interactions and associations with other important characters or important places/events will. (Note that it's the connections that are important. Extra detail that's unique to the character and doesn't connect them with characters/places/events that the reader is already interested in will be promptly ignored.)
That's a sampling of how you can parlay memorization advice into advice for helping your readers remember your characters and settings. There's likely more tricks you could use, so I'd recommend reading up on memorization aides, and thinking about how they might be applied in structuring your writing.
