Quests will normally lead you to enemies in Abysswalker. This is a great way to farm for experience and level up your character. The enemies aren't necessarily infinite, but they will respawn at a fair rate. Smack them around with your sword and gun.
When you do this, you'll see your level go up. Really, after getting through a few quests and taking out some foes, you'll be levelling fairly quickly. On top of this, it's just fun beating down on enemies, especially with the cool attacks that your character uses.
So, in short, have a little fun with these poor souls and rack up the experience. You won't be able to rely on this all of the time, but when it comes up, take full advantage of the situation.
We eluded to this a little bit already, but completing quests also levels you up, as you'd expect. There will be times where you just need to go through dialogue to gain some experience. Other times, you'll need to eliminate enemies and fight against bosses.
But, when it's just a little dialogue burning, then it's the easiest experience you'll earn. You'll see your level and your power rating get a little boost. So, it's pretty nice. You'll be building yourself up by doing something that's necessary for completing quests.
You know how it goes; in some games, you'll need to do certain side things to level up in different areas, but here, just keep doing what you're doing. You'll be a powerful, abyss-walking bounty hunter in no time.
In Abysswalker, you can upgrade your character's stats over time. This can be done by doing some of the things we mentioned above, such as defeating enemies and completing quests. This also correlates with your power level as well.
But, one other thing that helps with all of this is Haste Blessings. These blessings boost your abilities in different areas. They also can contribute to your stats and overall power level. One way to unlock these is by defeating bosses in the game world.
After completing different quests, you'll take on a boss. Continue on, and complete more quests and you will battle another large foe. Rinse and repeat, and you should have some rewards, including Haste Blessings and improvements to your stats.