My method is similar to what
@Emily_Babbelhund has written above, except I don't lure forwards from a sit. That's because I'm very picky about what I want my stand to look like - I want it to be a "kick-back stand", meaning that the front feet stay in position and the back legs step out into place. The reasons for being fussy are (in no particular order):
1. Good for rear-end awareness
2. If the dog learns to stick their front feet to the floor when changing positions, they will remain lined up with you if at heel. So kick-back stands, tuck sits, and fold-back downs are more precise than the alternatives, where your dog will be moving relative to you with each movement.
3. Because the stand (and sit, and down) can be initiated by either the front end or the back end of the dog, choosing one of these movement patterns is far clearer for the dog to learn. Otherwise you're using the same cue for two different movement patterns, and that's a cardinal sin in training - multiple cues for one behaviour is OK, but it is not OK to have a single cue meaning more than one thing.
4. It's preferred for Rally, Obedience etc.
To start with, I do loads of reinforcement for standing on a mat or good-sized placeboard. It's good to have a specific "stand" platform in the early stages, especially if your dog is used to sitting on a placeboard. Build that reinforcement for standing still in position - as
@Emily_Babbelhund says, feeding at chest height. Then you can start to feed above the head to lure the dog into an uncued sit. I don't use a cued sit because that means "sit and stay sat until I tell you to do something else", so I don't want to introduce them breaking that behaviour. Hopefully, if you've reinforced the stand enough, once you've lured and fed the sit, the dog will pop back into a stand. Click the movement of the back legs going out, and reinforce back into the sit, so you get nice "loopy training" going on.
Once you have that, use a smaller front foot target. Again, start by heavily reinforcing the front feet on and still. Work on them "sticking" to the target, by luring the dog's nose so that she stretches ever so slightly, C&Ting before she moves her feet. You can also drop food on the floor etc and reinforce for her keeping those front feet on the target and still. You should be able to build it up so that she really reaches for a piece of food in your hand, without moving those front feet at all. Once she has the idea, you can lure her into a sit and, as before, wait for the kick-back stand. If she gets stuck at any point, toss a reset treat behind her, then start with reinforcing in place in a stand again.
Once she's popping up in a kick-back stand reliably, you can put it on verbal cue and fade out your platform.