If your planer comes with a side fence, use it when planing an edge such as a door to aid stability and keep the planer from tipping as it runs along the edge.
As with hand planing, keep pressure on the toe or front of the planer when starting the cut and transferring the pressure to the heel or back of the planer as the cut finishes. This will help minimise any snipe from the planer as it makes its cut.
If you encounter a piece of debris that puts a small nick in the blades which leaves tram lines on the final finish you can get over it by nudging one blade over slightly to counteract the nicked blade.
Take care in doing so to ensure the blade doesn't foul on the casing of the planer body by rotating the block freehand with it unplugged.