You want to see good color, medium to dark green leaves.
Leaves should be somewhat "perky", like a teenagers tits, either poking straight out or just a bit up. Preferably not drooping.
Pistils should start building up and as they do you will notice the buds starting to form.
I can give better pictures later but my Hydo plant took off out of no where idk where it came from lol. she took up all the space in my room!