Genshin Impact is a game that wants you to stay busy. There's some debate as to whether or not it succeeds in keeping you occupied at length, but that point of contention aside, it certainly employs a wide array of tools to try to make you log in daily (or twice a day for you diligent resin-hounds out there), even if you're online for ten minutes at a time.
Commissions, boss fights, and limited events are among the carrots that Genshin dangles in front of you on a daily basis, and in exchange for tackling these chores you'll be awarded primogems, adventure ranks, and friendship levels. Farming for the former two has already been covered at length, but what about friendship levels? How can you unlock your main's voice lines and name card quicker? Read on to find out.
7 Ley Lines
The good news about farming for friendship levels is that companionship EXP is earned (albeit in small amounts) in parallel with nearly every other resource for which you'll be hunting — mora and character EXP included.
Because each traveler's priorities are unique, there's no way to rank the efficacy of every method for farming companionship EXP, since it's always given as a tertiary reward for farming some other resource. In this case, ley lines are where you want to be if you're about to build a new character, since ascending characters and enhancing gear is extremely EXP scroll and mora-costly. Be they blue or gold, ley lines dole out the same modest amount of companionship EXP to your party members, and that number increases with world level: 15 EXP for world levels one to four, and 20 EXP for five and up.
6 World Bosses
World bosses, or normal bosses, are where new travelers cut their teeth and hone mechanical skill — they're intimidating at first but quickly become routine since farming them is necessary to ascend your characters.
Not only will the world bosses rain down heaps of (hopefully useful) Gladiator's Finale gear while you collect elemental gems, they'll also reward you with companionship EXP for your party -- 30 EXP for bosses before world level five, and 45 EXP for bosses afterwards.
5 Weekly Bosses (Supplementary)
Genshin's three weekly bosses, or trounce domains, can't accurately be described as an efficient means for farming friendship levels, since they can only completed once between each Monday at 4 a.m. EST.
With that said, the weekly bosses are always useful, and should be considered high-priority to-dos even for infrequent Genshin players, since they offer a larger chunk of companionship EXP alongside their unique boss drops. Weekly boss friendship EXP increases by chosen difficulty from 50 to 75 per successful run.
If you're among the lucky few to get relevant artifacts from boss drops alone then you probably didn't need to pay much attention to domains until later world levels, when element-specific artifacts become more important. If that's the case, and you stuck with four party members through the entire game, then you probably already reached friendship level 10 with your characters without even trying.
For the unlucky majority, however, friendship leveling and artifact grinding are concurrent sentences — with one unlikely to be complete long before the other. The bright side, however, is that grinding for artifacts boosts your friendship level simultaneously. Domains gift you a paltry 15-20 companionship EXP depending on your chosen difficulty, but you need those artifacts anyway so it's better than nothing. Horde your fragile resin until you reach this stage of the game to speed up your friendship and artifact farming.
3 Daily Commissions
The commission system is frequently derided as Genshin's "designated fun quota" by the community, and not without good reason, repeating generic "deliver this here, punch that thing there" busy-work is tedious. However, your daily commissions are the quickest way to earn just about every reward they provide, the only downside being that you can only complete four everyday.
Companionship EXP, not unlike primogems, are rewarded after each discrete commission, and then given in greater numbers again for turning in four commissions to Katherine. Companionship EXP increases from 15 to 60 per commission based on your rank and difficulty of the quest. The lump sum awarded for doing all for daily commissions also increases from 45 to 100.
2 Random Event: Cuijue Rotation
These final two methods are the the most important, but also least well known, steps in expediting your friendship level farming. Even if you've only played Genshin for a few hours, you've undoubtedly come across "Random Event" quests (denoted with pale blue markers, only on the mini-map) that crop up as you explore, seemingly without rhyme or reason.
As it turns out, Random Events aren't all that random and can be triggered simply by logging in and out repeatedly at set positions on the map. Head to this beach on the edge of Cuijue Slope, facing the foot of Mt. Quince and Wuwang Hill, to repeatedly exit to the login screen to respawn new Random Events. These events will only give companionship EXP ten times each day, but you can spam them ad infinitum to earn rare drops from cicin mages, treasure hoarders, etc.
1 Random Event: Wolvendom Rotation
Mondstadt also has its own designated Random Event farming spot and it's reached by simply teleporting to the upper Wolvendom waypoint (physically higher and elevation, and slightly northwest of the beach also in Wolvendom). Note that for events where an NPC is spoken with, regular mobs in the vicinity need to be cleared first before the event can begin.
Completing events both at the Cuijue Slope location, and in Wolvendom, will reward 10 companionship EXP each below world level six, and 15 each afterwards, for a total of 100 and 150 EXP respectively assuming you repeat this trick ten times daily. Since these mini quests cost no resin and little time adding them to your friendship farming routine is a no-brainer.
There's also a smaller DLC allegedly coming later this month.