Leveling up quickly in Horizon Zero Dawn is a top prirority for those that want to get to the good stuff fast. As you play through the game, Aloy will gain levels, which award skill points that are used to improve her combat prowess and her stealthing ability. By focusing on a few key areas, players will be able to level up fast, making Aloy a rather powerful Nora hunter.
Where to get experience
Almost everything you do in Horizon Zero Dawn will net you some kind of experience, be it hunting animals for a trifling amount, or completing larger questlines for heavy experience. Main storyline quests and some of the larger sidequests will grant the largest XP bonuses, and many also come with a bonus Skill Point on top of the one you'll earn if you level up. Those can be time-consuming, though, especially in the case of quests that require you to journey to a new area of the map without a nearby fast travel point.
To rack up experience without questlines, try targeting larger machines. Once you've found a spawn location for robots like the Stormbird, Behemoth, or Thunderjaw, they'll appear on your map for easy location. You can go back and challenge them repeatedly, and once you find a good rhythm for taking them down, these are easily repeatable.
Best way to level fast
Main story quests and higher-level sidequests dole out large amounts of experience, usually with several steps that each grant their own XP bonuses. Some specialized sidequests are also very high in value, such as completing the Cauldrons, destroying Bandit Camps, and completing Hunting Grounds challenges. When exploring a new area be sure to check every green "!" symbol you see on the mini-map, so that you have a queue full of quests to complete at any given time.
If you don't mind slower progress and want to be all Aloy can be, take your time riding from place to place during quests and taking down packs of enemy machines as you see them. Getting in the habit of doing this will net you the cumulative experience from beating down machines, as well as the quest experience.
Gaining more skill points in Horizon Zero Dawn by leveling up fast requires a bit of work. However, by focusing on taking down tougher machines, and completing the main storyline quests, you will be rapidly rising through the ranks. Be sure to check out the full Horizon Zero Dawn guide for more on how to spend your newfound Skill Points, how to override new machines by finding all the Cauldrons, and more.