Level System
We use a simple Experience level system, like most games when you get enough experience you get a new level.

Each time you gain a new level your experience is set back to 0 and you then need to get more experience to level.

Experience can be gained from any number of things, Combat, Crafting, Auxillary skills etc .... and the amount of experience you gain is usually relative to the Level of monster your fighting (have selected), or Level of item your using.

This means as you level up you come in contact with higher level items and monsters and therefore your experience gained from performing an action will go up the higher level you become, the experience formulas are written in such a way that while the experience requirement to next level goes up the amount of effort needed is static so basically the same amount of time and effort it took to get you from level 9 to 10 is the same amount of time and effort it will take to get you from level 999 to 1000.