In general, when you are faced with difficult physical activity and you'd like to do it more efficiently, one of the tried and true methods of increasing efficiency is to repeat the activity over the course of several weeks or months until it is no longer difficult. This is often referred to as "exercise" (source):
- physical activity that is done in order to become stronger and healthier
- a particular movement or series of movements done to become stronger and healthier
- something that is done or practiced to develop a particular skill
If the walking technique in general is causing any confusion, one rule of thumb I personally like to remember is "left, right, left, right", although some choose to start with the right foot instead. In snow, while more effort may be required, the general idea is the same (with practice and a little luck, this "alternating foot" technique can be applied to mud, sand, and many other terrains as well).
Essentially, it is something along these lines:
You may have to lift your knees slightly higher because the laws of physics dictate that your foot and the snow cannot occupy the same space at the same time and so it will be resisting the motion of your feet, but the most important thing to remember is to keep up the alternating pattern (you can get yourself into trouble quickly if you attempt "left, left, right, left" -- I've seen it happen, and it's not pretty).
There are a couple other hacks you can try as well to combat physical exhaustion. In particular there are three techniques known colloquially as "drinking water", "eating food", and "taking breaks" - over the long run these can ultimately increase efficiency. Alternatively, if all else fails, there is one I personally refer to as "turn around and go back home".
Of course, proper equipment can also help, and the consequences of intentionally hiking 20km in deep snow with hiking shoes should not be unexpected. This was discovered roughly 4,000 years ago, and that solution has survived the test of time for good reason.