1. Length--Snow is softer than ice or pavement. Skis need to be longer and wider than skates so that they don't sink in too far. This means that you can't cross over.
2. Ski poles--Snow has more friction than ice or steel bearings so using ski poles helps. Using ski poles means that you need a more upright and forward stance than you would use for speed skating.
3. Ride a flat ski--While an ice-skate blade is fastest on edge, a ski is fastest when it is flat. Digging with the edge displaces to much snow, so only edge briefly at the end of the stroke.

Here's a cross section of a ski and a skate. The skate edge rides on the surface while the ski edge sinks below it.

Skate skis don't have metal edges. I bet you are surprised. Metal edges would be an advantage on ice but on snow they only add weight.

Your heels are free on a skate skis much like a clap skates.