Endurance is the easiest to level its progress depends simply on the distance traveled while not overweight. Just pay attention to the color of your weight, that it isn’t yellow. You gain most skill XP for the first few stamina bars, but there is no XP cap, so you can keep trying to level it (albeit at a slower rate) constantly all throughout a raid. Holding your breath also levels your endurance. If you’re sprinting, try not to get your stamina drained completely as you might be punished by fatigue which will decrease your stamina recovery. Some people suggest using stimulants to increase the speed of progress but it’s just not worth the cost considering how quick and easy it is to level endurance anyways.
I suggest leveling both Endurance and Strength together at the same time and passively while you play. Just stay a few kilos away from being over weight; so you start off training endurance, and then as you play and collect loot you’ll become overweight. Check the strength guide for “weights” you can put in your container.