Terrible advice, don't lean back and DON"T use your upper body to steer. Skiing way in the back seat and pivoting turns is the universal position of park rats/ east coast groomer skiers flailing around skiing powder for the first time, what ever makes you happy but you'll look like a huge boner and it'll take you a lot longer to get better.
Here's some advice from someone who skis more pow in a year than most skiers see in their life.
1) Equipment. Its nearly impossible to learn how to ski powder on short, skinny rentals if you only go a couple of times a year. Don't get normal rentals, get the high performance or demo package. Normal rental skis are usually shitty skis designed for beginner skiers who never leave groomers. Once you get the demo package choose a ski between 110- 120ish underfoot with camber and rocker (good choices to learn on would be S7's, JJ's, bentchetlers, DPS 112s, etc.) And choose a longer length than you normally would. High 170s and low 180s would probably be good to learn on unless you're really tall or heavy.
2. Keep your weight evenly distributed between your skis. Most people coming off of groomers put most of their weight on one ski when turning. Distribute your weight more evenly.
3. Don't lean back, stay centered on the ski, or even better get forward especially on longer rockered skis. Most people ski powder wayyy to far back, even some western skiers who ski a fair amount of pow. It kind of works but you loose a lot of control and the ability to slash and butter smoothly.
4. Don't pivot your entire body to steer, keep your upper body still and faced down hill and use your legs to turn. This is really important but hard to learn by yourself.
5. Take a lesson or two, its hard to learn how to ski powder by yourself if you don't ski powder very much. Being good at powder skiing is what makes it fun, and if you can only skid around in the backseat you'll never really understand why people compare pow to sex. Its worth spending the money to get good.
6. SPEED is your friend, the faster you go the more you float.
Life is brought down to the basics: if you are warm, regular, healthy, not thirsty or hungry, then you are not on a mountain. Climbing at altitude is like hitting your head against a brick wall... it's great when you stop.
Leave no turn unstoned.