Daily Commissions: These four tasks per day are well worth your time, because each one of them rewards you with either 175, 200, 225 or 250 Adventure EXP (depends on your Adventure Rank). If you complete all four of them and report back to Katheryne, you will also get an additional bonus of 500 Adventure EXP, so be sure to complete them.
Bosses: If you’re done with your Daily Commissions and want more EXP, hunting bosses is your next option. Go to the ‘Bosses’ tab in your Adventure Handbook and pick your target that awards Adventure EXP. Defeating one of the two Ley Line Outcrop bosses in the Mondstadt area is a good choice, especially for new players. They are low-level and defeating them may grant you 100 Adventure EXP. If you’re further in the game, try the elite bosses for 200 EXP instead, or the weekly bosses for 300 EXP.
Domains: They are located in temple-like entrances. The one-time-only Domains, of which the first one is unlocked at level 12, are a great way to start. Their rewards range between 200 and 500 Adventure EXP. However, as the name says, you can only get the reward once. Don’t worry, there are repeatable Domains like Cecilia Garden, Domain of Guyun and many more and yes, you will also get Adventure EXP every time you complete one. Although this can take a lot more time than, for example, defeating a Ley Line Outcrop, Domains give you plenty of other rewards, like artifacts for your characters and weapon materials for ascension.
Adventurer’s Handbook Experience: Unlike the options mentioned above, doing the experience tasks in your Adventurer’s Handbook cannot be repeated. But on the bright side; the Adventure EXP rewards are quite big and don’t require a lot of time investment.
Exploration: The open-world of Genshin Impact is filled with many Teleport Waypoints, Statues of the Seven, and Domains which you can discover in return for a small amount of Adventure EXP. If you enjoy wandering across the beautiful Genshin Impact map (and the great music as well), this is a great way to level up. You can also search for Anemoculus (in Mondstadt) or Geoculus (in Liyue) orbs. Offering these to the Statues of the Seven will reward you with a lot of Adventure EXP, but again; it takes time and it can only be done once.