I was finding it very difficult to turn from heel to toe edge on steeper slopes.
This seems to be a pretty common problem even on more gentle terrain. In my limited experience teaching others (I'm not an instructor or anything) this is mostly due to the fact that beginners tend to lean back
or hold their center of gravity more towards the tail of the board, rather than keeping it centered. When you're driving from the back seat like this it is very hard to initiate the carve on your toeside.
However, I noticed that I got really fed up by the end of day because whenever I was succesful in getting onto my toe edge, I feel I had no power in holding the edge. First I had to really push down hard on toes and knees to get onto the edge. When I tried to hold it, my calves started to really burn.
Sounds like fatigue. Snowboarding (like most sports) is going to use muscles that you rarely use, and it is going to use muscles that you commonly use in ways that you've never really used them before. It does take time to get conditioned for this activity.
I look longingly at other people whizzing by me, effortlessly getting onto their toe edges while I'm in pain.s.
Aside from fatigue & conditioning this is really a reflex & muscle memory issue. The more you do it, the more effortless it will become and the less you will have to think
about how to do it properly; it will start to come more naturally.
Most people can do a heelside carve, or they can do a toeside carve, but they have trouble going from heel-to-toe. I think it is mostly mental - like you're thinking "I've gotta turn all the way
over to toeside now OMG!"
Just block out that "OMG!" feeling that comes when you're traversing heelside, and just initiate a toeside carve like you normally would - remember not to lean back! - only you'll hold it a little longer to come around beyond the fall-line.
Maybe this doesn't make sense or maybe it's not the best advice but it has worked for a few people that I've worked with