As you get deeper and deeper into Genshin Impact, the more you have to prepare and think about what your next moves are in terms of progression, particularly if you're not spending money on the game. As your world level increases, so does the toughness of the enemies you face, and so you'll need to make sure you can still take them down, whether that's with friends or by yourself.
At Adventure Rank 35, the game should still be pretty manageable in terms of difficulty no matter what characters you are using, which makes it a perfect time to start preparing for World Level 6 and getting ever closer to maxing out your characters. Read on below to figure out the best way to do this.
Get your carry to level 80 asap
If you've been following along previous progression guides, you'll know that the most important thing in your adventurer team is having someone that deals a lot of damage. This continues to be the case, as the majority of Genshin Impact's content revolves around killing things quickly.
Specifically, your focus should be on your main dps adventurer, which is to say whatever character you consistently have out on the field of battle duking it out with enemies. Beating world bosses for ascension materials is only going to get more difficult from now on, so prioritizing them now saves you the headache of being significantly underleveled while battling level 83 world bosses at world level 6 (especially if your main dps is a hydro that needs to kill Oceanid).
Partially build up supports
Obviously, your carry can't do everything alone, so you'll need to build up some other characters for your team to help out, but you don't need to worry about leveling them too much. In fact, you should avoid that so you don't find yourself running low on Mora or some other currency.
A good rule of thumb for leveling support characters--particularly ones that only pop into battle to use an elemental skill or burst--is to build them up 20 levels below your fully-leveled carries. This is to say you should bring your healers, enablers, and reaction setup units to around level 60 if they aren't there already.
Don't worry about artifacts for now
If you've been doing ok without leveling/worrying about artifacts for now, keep doing what you're doing. The absolute best artifacts in Genshin Impact are the of the elusive five-star variety, and those become less elusive after getting past Adventure Rank 45. At that point (Rank 46+), your world level increases to level six, which unlocks artifact domains that guarantee five-star artifact drops.
This isn't to say you should completely ignore artifacts. They are important tools in customizing and maximizing your adventurers' abilities, after all. But don't get worked up about farming artifacts to make the ideal kit now, because that gets much easier once your access to five-star artifacts really opens up.
Redeem story keys
While you may have gotten access to a few special, character-specific quests in Genshin Impact up to this point, you truly unlock all of the game's story content (as of this writing, anyway) by the time you hit Adventure Rank 40. These quests require a special item known as a Story Key, which you can collect by doing Daily Commissions. Using these keys lets you explore the backstory of characters like Venti and Mona or even relative newcomers like Childe and Zhongli.
As an added bonus, all of these quests give you access to trial versions of these characters, which can help you determine whether or not you want to roll for them.
Co-op gets more and more important the further you get into Genshin Impact. And--while it's not super crucial to have friends for domain challenges (since the game has matchmaking there)--it may be worth jumping into people's worlds and offering to help them in hopes they may at some point return the favor.
This is especially important if you're finding yourself having trouble with any specific world boss. There is zero matchmaking for these challenges, yet they are so much more fun (and manageable) with a partner or three helping you complete them. If you want to make sure you can clear every possible challenge in the game for your characters, it's wise to try and find players of a similar world level that you can partner with whenever you're playing.
Think about farming progression
In preparation for world level 6, you'll want to think about maintaining a roster of adventurers that can help you for whatever artifact runs you need to complete. This means having an adventurer for every element (if possible) so you can take advantage of any elemental buffs that you'll need to help you clear these level 90 challenges.
This doesn't mean you should go ahead and dump resources into a dps for every element (in fact, do not do this). It just means you should have a plan to slowly but surely raise up a character that can meet the demands of every domain. This likely will start with your leveled dps character, but then extend to a character who's element aligns with the domain challenge rewards that are best for your dps.
As an example, if you are using Ningguang as your main dps, getting a set of quality Archaic Petra artifacts should be at the top of your list. The domain challenge for getting these artifacts is the Domain of Guyun, which highly favors Electro adventurers, so you may want to think about building up someone like Fischl or Beidou to help you more easily kit out Ningguang.
Thinking about this progression strategically will help you be more efficient when it comes time to getting artifacts, which will be the keys to maximizing the potential of your team as you head toward even tougher challenges.