My thoughts and things I've done:
Multiple establishments of important items, Chekov's Guns and what not. Always useful, especially if props are important. Someone having a gun, or knowing that someone is good or bad with guns because it has been established in some scenes prior can add a lot of tension in a scene where a gun is drawn and we can't tell if they're going to totally wuss out or go through with something terrible. Give something a panel if it is important, and if it shows up again; put in the scene prior to it being brought up but don't draw too much attention to it until it is needed. It can lead to a good pay-off. For The Sisters, we've got a thing trapped in the basement that shows up in Issue 1, lays silent until Issue 3 (where our protagonist silently tells it to hush while a hot guy is down there) and finally talks again in like, Issue 6. It's that middle item where it is present and does nothing that tells the reader we know it is down there, but it isn't coming up yet.
Watch a mystery movie or a thriller and you'll see this happen a lot. Watch "Suckerpunch" if you want to see how to establish a lot of good props that have absolutely no value on the plot and really suck at being useful; but are still well established by way of the camera. Or watch Daredevil in the first season, Wesley does it with his gun and it is nice imagery pay-off.
When it comes to characters and character development, it may also help to show off a new dynamic by putting characters in a similar dynamic but with a different character. I'll toot my own horn here: We established our Zak Bagans-expy, Craig; as being a huge jackass when it comes to hanging out with his little brother and his girlfriend's little sister. We eventually get to see Zak interacting with his girlfriend and his best friend; during which he is a much more agreeable and fun person. Later we see him hanging out with both groups at the same time and he's pretty much splitting the difference in attitude. It feels like logical progression, it is something we can buy into. He's a jerk, but he's not always a jerk, and when he is with his friends and the people he's a jerk too; he is something less of a jerk.
I'm not big on flashbacks or monologues proper especially for the purpose of exposition. If someone ever gives exposition, especially to hint at plot points or previous plot points; don't make it feel forced. If someone is talking about a plot relevant event we've seen, show how they feel about it. People react. We did a murder and when people talk about the killing or the man who was killed, they talk a little different colored by their own actions and how they remember him. This also helps show the reader that the event had purpose and the cast sees things differently from one another, which does justify how the reader may view the deed differently than the characters too. It'll remind them to remember how they felt.
Linking pages helps too. I've found I often get by with making a pun regarding something that shows up later. People will remember my terrible dad-tier joke in the description and when it comes up they say "Oh god damn it." One of our big fans got very upset when I made a bunch of word play regarding a character she liked; all of which related to getting killed. Of course our baddy also leaves a lot of hints at him being bad that are really only apparent on a second reading; so people noticing the word choice like "take care of the girls" rather than "see if the girls need help" becomes a hint of things to come and sort of a reminder of what is going down.
OBVIOUSLY, if you go super far ahead and are in like, multiple hundreds of pages and years of length; re-caps and such are probably needed. But you can get by with less effort right now. Focus that on making sure people are reading your work in the now, rather than making sure people will read your work once there's more of it. But that's just my thoughts on it. I'm aware not everyone puts out multiple pages each update, so not everyone works with a very direct scene-by-scene framework.
I guess, don't expect people to remember -everything- but if they need to remember something; make sure it has some importance. Even our least important prop had a panel to it that spelled out clues; and I think it was easily forgotten because everything else around it was far more intense.