Ok, stealing retrogrouch's paradigm
1. Deflate your tire but keep it on the rim.
2. [Run a tire lever around the wheel on each side of the tire between rim and tire (to break any adhesions.]
3. [Use a soaked sponge to get soapy water in between the tire and rim at all points]
4. [Push your valve stem straight into the tire. Probably not needed for tubeless, but you should be sure that your valve stem is properly aligned so that it isn't preventing seating of the tire.]
5. Reinflate your tire [by seating them, then gradually inflating and making sure that the little ridge around the tire sidewall shows that the tire bead is seated equally at all points.]
To emphasize: there usually is a little ridge on the sidewall that shows just above the rim. If that ridge is equidistant from the rim at all points, the tire is seated pretty much properly. If that ridge is obscured by the rim that means that the bead didn't slide out enough at that point to seat. It's usually pretty clear.