When considering how to maintain or sharpen your knife there are 2 things to consider before you begin:
1. What steel is my knife (or knife core) made of?
2. What is the angle of the blade (edge) itself?
Once we know that answer to these two questions we now how to sharpen the knife.
The first consideration is the composition of your blade. Whilst not all blades comply typically Japanese blades have higher carbon (north of 1%) where as western knives are much lower (around 0.5%).
What's the difference?
The elevated carbon (Japanese knives) content makes the edge much harder but also more brittle. For brittle yet hard knives you need to use fine whetsone cooled with water, for low carbon you sharpen at higher speeds with a more brutal approach. Neither is the correct method - the method applied needs to match the knife being sharpened.
Knife Edge Angle?
This is the simple part.
The angle at which you hold your blade while sharpening must match the angle of the blade edge. Knives can vary anywhere from ~11% up to 30% so if you are sharpening an edge set at 11 with your tip at 30% you are blunting it. Most Japanese knives are set around 15% (this can be done so sharp due to the sharpness of the blade) where as most western knives are closer to 20-25% (they have lower carbon and therefore will bend on the edge if it's made to fine. For heavy choppers (or champagne sabers) you don't want a fine edge, you need something tough so it approaches 30%.
This all sounds tricky but it's usually on the box or online information from the brand. So have a look at what the edge is and thats the angle you need to follow.