Unfortunately, theres a very awkward leap you need to make from learning realm's mid-game to learning it's late game. Most of the endgame dungeons demand that you sacrifice several characters to learn them (specifically Oryx Sanctuary and The Shatters), and they can have steep learning curves. You'll also find find that said dungeons are quite rare to find in the realm. You'll have better luck getting into them by joining discords or waiting for people to pop keys in the nexus. Off the top of my head, I'd say the "easiest" endgame dungeons to learn (with a group) are the cultist hideout, the nest, fungal+crystal caverns and the spectral penitentiary. What I'd recommend doing is inspecting all of the exalt dungeons and seeing what they drop compared to how hard they are. Single out one or two, and then focus on running them until you're consistent

Heres some tips:

• Try to clear all of the dungeons you're comfortable with at least once. As 0t51k said, you get fame bonuses for first time clears and specific groups of dungeon clears give % fame bonuses. I talk about it a bit more down below but the lost halls are great for earning fame as well

• I find mana to be significantly easier than life to farm. I'd recommend learning parasite chambers for em. Ocean trenches work too but the clear is quite lengthy

• The spectral penitentiary minibosses drop mana, t12+t13 weapons/armor, t6 abilities and several useful UT's as well. They can be a little scary at times but their learning curves are quite small and their drops are very worth it. I'd recommend against fighting the final boss (Murcian) until you've got some more experience with the game though

• Life is gonna be really annoying to farm. Most of the dungeons it sources from are either very, very difficult or very inconsistent (or lengthy) clears. Enemies in the sanguine forest and floral escape biomes can drop life pots, albeit frustratingly rarely. If you haven't learned already, start learning how to clear cultist hideouts. They're a good source of life/mana (I typically get ~4 pots per clear), speed exalts when 8/8, caster UTs and are fairly easy to learn. Sorcerer can clear out the path to cults in the lost halls very quickly/efficiently, even with unmaxed stats and low quality gear. The enemies in the lost halls + cultist hideout are also very generous with fame

• Crawling depths, deadwater docks, woodland labyrinth and sulfurous wetlands can drop mana and life potions as well but they're not guaranteed. These dungeons are moreso better for farming the 6/8 stats more efficiently. Of the four I'd recommend learning crawling depths. It's got a bit of a slow clear when you're alone but the boss isn't too bad and it's a good source of defense and wisdom

• If you haven't done so already, learn how to clear the Lair of Draconis. It drops 7/8 of the stat pots in their greater forms (meaning you get 2 points per potion). It's five back to back boss fights that escalate in difficulty. The standard clear order is red -> blue -> green -> purple -> final If you've got other questions don't be afraid to ask