Ideally you make a cut at 45 degrees into the wood and then make another at the same angle reversed a distance of twice the log width from the first cut. This clears a chip from the wood and you repeat until the wood is cut. However unless the wood is small or the knife exceptionally powerful you will never open up a notch wide enough so you start multiple notches and clear them and then join them to make one notch. You can also work around the wood if you can turn it, but this is in general *NOT* a good idea for felling. You also have to adjust the angle according to how the blade is ground, but that is a general decent starting point. You also generally needed wider notches than are optimally necessary because few people follow cut lines exactly.
-Cliff