Listed below are strategies on how to counter one class with another class. Nearly every class in the game is capable of killing another, some with more difficulty than others of course.
Killing a warrior 1v1 is tough due to the nature of the Warrior. They have the most health, have a shield that can block anything but magic, and have a charged attack that can kill any unit in one use. The key to winning against them is evasive maneuvers. Staying out of their range is the only way outside of luck to have an edge.
Warrior: To counter a warrior as a warrior, it mostly boils down to who can kill whom first with their charged glaive attack. A stretegy to use is to wait for them to use theirs first by baiting them then moving away as soon as you think they'd attack, then counter with your own. If your goal is not to kill but to get by, switch to your shield and raise it by holding L1. Unless they hit your side or back, they cannot hurt you with your shield up.
Worker: To counter a warrior as a worker, you are going to rely on bombs. Early in the game you could use a charged axe to attack, but any warrior worth their salt will have their shield up in anticipation. After the upgrade, if you see a warror, stay at least half a screen away if you're out in the open, target them and spam bombs while jumping in every direction. If a warrior has its shield up, you'll do half damage but still slowly chip away. You are better off with resources around, such as logs, trees, metal, and metal mines as the warrior's dash can't go through them but your bombs can go over/by them and do AOE damage. Beware though that your bombs will move a resource or fall a tree so you may not be able to stay at one spot.
Ranger: To counter a warrior as a ranger, you need other people. The warrior is the clear counter to a ranger due to its high HP and shield, so naturally to kill a warrior you need to have them not have their shield up. However, you can kill a warrior with low health if you use your musket and charge it. It will do very little damage, but it will do some. If you're a ranger, steer clear of warriors if you're alone.
Mage: To counter a warrior as a mage, you have three options. Fast method, medium method, and slow method. Fast methos is charging your AOE fire magic and releasing it at the very edge of your range. It takes 3 fully charged attacks to kill, with burn out damage, and is best done on ice or around resources to limit where the warrior can dash at you. With your low health, you need to evade every attack or you will fall at the first good connection. Medium method is freezing with a charged AOE ice attack then unleashing a charged AOE fire attack. Repeat if you're around resources, or commit to the fast method if not. Slow method is repeatedly using full charged AOE ice attacks to chip away at its health. Remember, your AOE has a high vertical tolerance, about 1 character higher/lower than you, so if you can, fight around a ledge so you can drop down and jump up when needed to avoid getting hit.
Priest: To counter a warrior as a priest, you need to be a dark priest. You may think just to life drain till near dead then strike with your rod. This is not the best method. USE. YOUR. CHARGED. ATTACK! It does not take a full charge to work, about 1/4 is fine. The attack, called Curse, will cause the warrior and others to be unable to lock on to you and run straight. Hit it with Curse then life drain. Repeat till it is almost dead. If it hasn't retreated yet, strike it with your rod when it is cursed. However, as a priest you are better off not running off by yourself, so if you know people are behind you, curse and fall back.