I just started snowboarding last year and this is how it went down for me.
I found videos from this site
while browing youtube and watched them all. They cover everything really well and some of the stuff on there you can do without going to a hill. For example, skating and stepping
I watch all of the 9 Beginner lessons numerous times before ever stepping on a hill and I am pretty confident it helped me a ton. I knew in theory what I was supposed to do with my weight, pressure to use to turn, etc. I had all the theory in my head, but didn't put it to use right away.
When it came to my first day I took a lesson which is something everyone should do. But the great part is that I already knew 90% of what the instructor was talking about. I just wanted FREE lessons on the net that were jam packed with detail. I knew the theory behind what I needed to do so now in the lesson I didn't need someone to tell me push here, pull here, lean here, etc. I knew how I was supposed to move and the time in the lesson was spent troubleshooting minor things.
Save up enough money for a lesson
Prior to the lesson watch those videos
Practice what you can at home
After the lesson, practice practice practice.