Learn backflips first, they're a guideline for flat 3s. Flat 3s are basically just a slight tweak in the movement of your shoulders. Get a bit wider stance than a backflip and wind up your arms like you're gonna do a 360 spin. Coming off the lip, pop hard as fuck and throw your arms up and slightly in whatever direction you're more comfortable with. Look up to the sky with your head twisting whatever direction you're spinning/inclined to. Bring your knees to your chest (this should come naturally) to speed up the flip. Coming around you should feel your rotation slowing down and be able to see your landing. Spot it and let your feet come down to meet the ground (this should also be a natural movement.
Some things to notice:
- Don't force the tuck in your knees, they should come up to meet your chest naturally if you commit to the flip, if you overthink this you'll stop your rotation mid flip.
- Make sure you have a firm base when you're landing, it's easy to carry too much momentum through the landing and wash out.
- Get a HUGE pop, the flip generates in your legs. Pop, then flip.
- Use your shoulders/head to guide your body back to an upright position for a solid landing.
Good luck homie!