I use a number of methods,
The two main ones involve a Japanese water stone, this takes practice to get the angle right.
The easiest method I use is with a pocket ceramic sharpener, this has two 'grits' a medium and a fine. Both sets are at the correct angle and it does get a razor edge on most of my blades, particularly my Helle fixed blade.
Dazz
PS the water stone is available from hardware stores, the ceramic can be bought from most fishing/hunting shops.