The Six Skills
1. Accuracy: Decreases size of crosshair slightly for each point, improving the accuracy of all weapons. The item Sniper Scope (Add hyperlink) adds 25% more accuracy when bought in the Shop.
2. Strength: Only allows one to buy certain weapons which require strength, gives no in-game bonuses at all.
3. Luck: Adds 1.6% to the chance of dealing critical extra damage above the maximum damage of the gun shot, maximum is 27.2% for luck artifacts.
4. Explosions: Adds around 100 damage to grenades, some explosive weapons require explosions.
5. Health: Adds 50 health to Max HP, maximum is 950 health points with health artifacts, maximum without artifacts is 600.
6. Defense: Reduces damage taken by 5% for each point, maximum is 75% with defense artifacts.
Tips and Tricks Tips on having good stats
When you make a new account and get to level 1 you get your first skill point and every level after you get another point. What you should do is increase your HP to 16 points. Once you do that, max defense then that last HP point. Time by time if you believe your accuracy is just that bad, upgrade accuracy to work towards a new gun, and strength is of course only for guns. Upgrade explosives once just for the cash if needed, upgrading a stat just for the cash can be a good choice too. For example, buying survival expert gives you 7 cash, but it isn't overall useful, and using it on HP and Defence, or Accuracy is far more profitable in the long run.
NOTE: Of course make sure to put points on other stats ONLY when you need to get a better gun and when you have the money to buy that weapon. Reason is because you don’t want to be say level 15 and still have only a glock. If you want to know if you have enough money for the guns you want you can check http://tdp4.wikia.com/wiki/Guns for gun prices.
Why max health?
A common misconception is that Defence is better to upgrade than HP, but this is not true. Defence only makes a difference when it is maxed out; HP gives you more survivability instantly. For example, at +5 defense and +0 health you die more quickly than if you are at +0 defense and +5 health. However, if you are at +10 defense and +0 health you die less quickly than if you are at +0 defense and +10 health. Even so, the time spent on increasing health is more worth it because you get to survive a lot more; the lack in defense is more than compensated by the increase in hp.
You should upgrade HP to 10 before upgrading Def at all. At 10/10 You should buy Defense artifacts before HP artifacts to help fill in the deficiency in def.