The following excerpt/paraphrasing was taken from the Community Collaborative Rain, Hail, & Snow Network website... www.cocorahs.org.
The ideal situation to measure snow is to use a snow board. A 16x 16 inch piece of plywood or wafer board is fine, and paint it white. If you don’t have one of these, that’s ok. You will need to find a location that is flat and level. A picnic table or wooden deck or porch is just fine, just be sure to take the measurements several feet away from your house. A sidewalk, driveway usually is not a good place to measure as those surfaces can accelerate melting. Grass is not a good idea either, because snow can sit on top of the grass and cause a false reading.
The National Weather Service measures snowfall about every 6 hours. If you can do that, that is great. If not, do it at your convenience. Snowfall is the maximum accumulation of fresh snow during the past 6 hours or past day prior to melting or settling. Since snow melts and settles, you may have to measure during or soon after snow ends in order to capture how much accumulated. You simply stick a ruler in the snow and take the measurement. It is a good idea to take it in 2-3 places, and then use the average as the snowfall total. Wipe the deck/board/picnic table of the snow, and then measure any additional snowfall, repeat if necessary.