decline plank ; crow stand
Start with a few seconds; rest for what remains of a minute; then repeat 5 times. Build up to 5 holds of 15s, with rests of 45s.
Again, start with a few seconds; rest for what remains of a minute; then repeat 5 times.
Keep alternating between legs.
Once you can achieve 5 sets of 15s with 45s rest, it is time to move one to the next step.
Again, build up to 5 sets of 15s, with 45s rest.
Once you've achieved that, you can start working towards holds of one minute. Aim for one minute work in total, so for instance, do 3 sets of 20s with 40s rest; or 2 sets of 30s with 30s rest. Keep building this up until your can hold the position for one full minute.