Sounds trivial, but getting up off the snow with both feet strapped in is one of the genuinely hard things on day one. People sit in the snow for ten minutes trying to muscle up. There are two tricks, one for heelside and one for toeside, and once you know them you never get stuck again.
Heelside (sitting in the snow, facing downhill). Bring your knees to your chest so the board is close to your butt. Grab the toe edge with one hand, roll your shoulders forward, and push the snow with the other hand as you stand up on your heel edge. Keep the board perpendicular to the slope the whole time or you'll slide away from under you.
Toeside (face-down, looking uphill). This one is easier once you know it. Flip onto your belly so the toe edge is biting into the snow. Get on your knees, push yourself up with your hands, then straighten your legs into a stand. The toe edge holds you in place while you come up.
Here is a clear demonstration of both:
Source: Snowboard Addiction · How To Stand Up On A Snowboard
Key tips
- Keep the board across the slope (perpendicular) so it doesn't slide while you stand
- Get the board close to your body. The further away it is, the harder it is to stand
- Rolling onto your belly and standing toeside is usually easier than heelside
- Use your edge, not your muscles. If you're grinding to stand up, your edge isn't biting
- Take breaks sitting on your knees (toeside) rather than on your butt (heelside), which is warmer and gets less wet