If you want to determine if you are sharpening at the same angle that the blade already has, try this easy trick. Mark the edge bevel with a magic marker. Then go ahead and do a stroke or two on the stone (or take a stroke with your Lansky, or whatever). Now pick the knife up and look at the edge.

A particular gentle and effective way of sharpening knives is to maintain their edge using a whetstone. WÜSTHOF whetstones consist of a high-quality combination of various abrasive grits. The stones have two different sides: One with a fine grit and the other with a coarse grit.
Use the coarse side of the whetstone to grind away any roughness.
This is the pre-sharpening stage. Use the fine side to give the knife its sharpness - this is the fine sharpening stage - and to polish the edge.
The finer the grit of the stone, the finer the edge.


Tips:

Always sharpen in the same direction, whether it's front-to-back or back-to-front.
Despite what its name might suggest, keep your whetstone dry. Using oil or water on a whetstone traps tiny metal particles in the liquid, which in turn produce a more ragged edge than when using a dry stone.
Don't believe the hype about knives that supposedly "never need sharpening." Cutting produces friction, and friction causes a knife's edge to lose its sharpness. There's no avoiding the laws of physics.

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