Project Zomboid has skills that are split up into 6 different categories. These categories consist of:
1. Passive - Strength, Fitness
2. Agility - Sprinting, Lightfooted, Nimble & Sneaking
3. Combat - Axe, Long Blunt, Short Blunt, Long Blade, Short Blade, Spear & Maintenance
4. Crafting - Carpentry, Cooking, Farming, First Aid, Electrical, Metalworking, Mechanics, & Tailoring
5. Firearm - Aiming, Reloading
6. Survialist - Fishing, Trapping, Foraging
With these skills in mind, here's the best ways to level up some of these skills that we know:
Sneaking is a great way to level up both your lightfooted and sneak skills. Overall leveling this skill up will make you more undetectable by zombies around you. If there are a lot of zombies around, find a place close by that won't get you killed and start sneaking back and forth and watch these skills level up fast.
Running around is a super easy and the fastest way to level up your um… sprinting. Duh. If you run around a lot, you'll start to run faster as you level up, which is the most important thing when you're running for life. Unfortunately, you won't be able to run longer than normal, but the extra speed will make up for this in the long “run”.
Probably two of the easiest skills to level up. Just find some dumbbells and start pumping iron. Make sure you have plenty of food and water nearby, since you'll need to refuel after a long workout session. Make that home gym a reality.
You can level up your choice of combat skill (depending on what weapon you're using) by just killing as many zombies as possible. While you're doing this, you'll likely level up your other skills such as sneaking and sprinting, so if you just want to grind levels, go to an area with a high population and some strong weapons and just start going to town.
These two skills can go hand in hand if you know what you're doing. Once you get a base established, you'll want to find somewhere with a kitchen and a nice, open backyard. With these two, you can harvest a ton of crops from your backyard and cook them in your kitchen. Continue to repeat the process and you'll have some of the best meals in the game for you and your friends to feast upon.
One of the easiest skills to level up in the game. If you have a firearm, even if it has no bullets, you can hold it and reload it, which will grant experience points. So the next time you're exploring, hold your gun in hand and just start reloading and watch the experience points rack up.