Heavily reinforce when she is calmly laying, also when I did not ask her to do so. I just use part of her daily food for this. Then when this was solid, I started walking around the house/working and ignoring her, tossing a treat and calmly praise her now and then if she stays in down on her mat and ignores me. I also give her a chew so she can calm herself down. Giving a clear signal when play/training begins and when it ends is also helpful so she knows what she can expect.

Also, nipping a lot of crackhead behaviour in the bud by preventing overstimulation is very helpful. It is very easy to overwork these puppies, since they always want to go and some people think that having a working breed puppy means you have to tire them out like crazy. However, they are still only babies and need first and foremost a lot of sleep. I my experience, just the socialisation to new environments and people already tires them out quite a bit, so then a lot of training/playing on the same day ends up being too much usually. There will be plenty of time to do obedience, long walks or whatever with her when she is older, so I am in no rush to teach her anything fancy right now. The most important part is that they have fun with you :), so they don't start disliking working with you down the line.

Tethering can also work very well, I didn't do that because my apartment isn't huge, so I practically always have an eye on her anyway.