In Witcher 3 you gain a new level by gathering enough experience points. Up until level 10, you must collect 1000 experience points for each new level. For levels 11-20 1500 experience points are required. From level 21 you will need 2000 experience points for each new level.
Experience can be gathered most easily in two ways. First, you can complete quests. Main quests and witcher contracts are giving you the most experience, although some side quests offer nice experience rewards as well. Additionally, you should regularly fight living enemies and monsters. Experience reward for killing a single monster is usually small, but by attacking a group of enemies or fighting frequently you can accumulate large amounts of experience.
Other interesting ways of obtaining experience:
- Destroying monster nests - the basic reward is usually small but an elite monster can appear near the nest. Killing him is well rewarded
- Securing abandoned places - usually you receive 100 or more experience points for such action
- Using Axii sign during conversation (special dialogue options) for a single use of this sign you receive around 30-40 points
Important! There is a very important relation in the game linked to obtaining experience. The game rewards you with experience only for performing actions (completing quests, killing monsters etc.) suggested level of which is equal or higher than yours. For example, if your character is on the 10th experience level and you will defeat enemy on level 10, then you will receive the standard amount of experience. If enemy is on the 15th level, then you might receive much more experience. If he is o much lower level (for example, 5th) then you won't gain any points at all. It is wise to always start with completing actions prepared for Geralt's current level. Thanks to that, when you gain new levels, you don't lose the opportunity to gain experience from some quests.