Skill points are earned when enough karma is earned. Karma is earned by defeating enemies and finding usually hidden karma sources which look like demonic bird feeders filled with boiling blood. Quickly, you ean earn extra karma in fights by:

• Killing waves of enemies quickly
  
• Using different weapons in the same fight
  
• Killing multiple enemies at once
  
• Harming or killing enemies using environmental damage (such as exploding barrels)
  
• Taking little damage
  
• Cutting or blowing enemies into pieces. You can continue to cut up a killed enemy for a few seconds after dealing a killing blow with your sword.

Here is a suggested order of skill points to buy, with reasoning. I will not name every skill, just the important, initial skills. After getting the skills on this list, what you do afterwards is both less critical and also up to personal taste.

• First, Richman I and II from the Luck tree. This will increase the amount of money you find, enabling you to upgrade your guns more quickly. Since there are a limited number of places you can find money, getting this as early as possible will enable you to upgrade your guns more quickly, and hopefully more fully.
  
• Next, get Kenshi and Kensei from the Katana Mastery skill tree. This will convert the sword from a good backup to a good primary weapon.
  
• The Circle of Iron skill from the same tree is your next choice. You can charge this attack while getting in the middle of a crowd and unleash a very powerful strike in every direction which will get you lots of bonus karma. This attack does a lot more damage than you would expect.
  
• The final important Katana Mastery skill is Aswang Hunger. This will let you keep your health up while swinging your sword. You will be amazed how your health seems to stay up as you take and deal damage in intense fighting.
  
• Next, get both of each of the Demonslayer and Godslayer skills. The "greater demons" of the Godslayer skill might seem to refer to bosses, but you will start to encounter greater demons in regular enemy waves starting around the middle of the game, so this is worth getting.
  
• Finally, the last important skills are Drain Soul and Soul Hunger from the Restoration tree. This will help save your life if you run out of health.

I'll also mention here some skills that should be low priority, and why.

• The movement skills will help you get around levels more quickly, but in my personal experience the default stamina amount and recharge rate are already more than enough, even if you are sprinting and hopping quite a lot. However, if you find yourself running out of stamina during fights often and suffering for it, you may want to prioritize these skills.
  
• Medic and Doctor from the Restoration tree give you the opportunity to go above your maximum health, but this is not much help since you can only do this when you have access to medkits and in the higher difficulty levels you will be healing frequently by other methods during battle anyway.
  
• For the same reason, the Control Pain skills from the Mind tree are equally unimportant.
  
• The Rage skills from the same tree are only good if you can carefully keep yourself at low health without dying, which is a tall order and probably asking for trouble.

The powers are purchased by spending ki crystals, which are found throughout levels. They are sometimes hidden in secret places, so make sure to look around before moving on, and double-check areas you must backtrack through for changes which might be opportunities, such as demolished walls.

• Unless you are playing on a difficulty level too low for you, the most important powers by far are the healing powers. Buy this whole tree first. This will enable you to effectively heal yourself during combat and keep yourself alive.
  
• Flux is the next most important. This skill allows you to incapacitate and dispatch enemies, and earn more karma while you do it.
  
• The last two trees are not very important. Shockwave is pretty similar in effect to Flux, and while Protection can be effective, it's often not worth the cost of not being able to use two hands and the movement speed penalty. What you do after buying the first two power trees is a matter of taste.

Weapons are upgraded by spending the money you find. The sword is the only exception; it is upgraded via story progress. Here is a suggested order:

• The first weapon you should upgrade is the Zi-Type 23 PDW (submachine gun). It may be tempting to upgrade the pistol, but these upgrades to not make it much more useful, so hold off. Akimbo first, then match grade barrel, then laser sight. These will enable you to do very high DPS, which is helpful for some boss fights and minibosses.
  
• The high-strain system on the Crossbow is next. This lets you charge your shots and do very high damage with very low ammo use. It can one-shot a few enemies, and you can put a lot of hurt on bosses and minibosses from a distance.
  
• The sticky bombs on the crossbow can help you earn extra karma with multi-kills, but does less damage than you would expect, so bear that in mind.
  
• The shotgun upgrades can make the weapon into a very powerful close-range weapon. Firestorm, then quad pack, then double shell clips.

If you upgrade in this order, and also get the Rich Man skills first, then you should be able to afford to upgrade the other weapons as you find them.

Good luck!