Unfortunately they've just missed them going on sale for next season, but a few thousand STs will go on sale for 25/26.
There isn't a waiting list and in recent years they've sold them on points in 21/22 (1000 -> 500 -> 250), sold them with no criteria at all for 22/23, and sold them using a criteria of 15 home prem games attended in the past 2 seasons for 24/25.
Because of the club's inability to decide on the right way to sell STs, I can't really give you perfect advice, but a few thousand STs will go on sale for 25/26 assuming the north stand is finished on time, so if they attend a decent amount of prem home games this coming season and they'll have a chance.
If I remember correctly, there were roughly 6000 in the queue when they went on sale last month, so you're looking at upwards of that number who would attend more than 7.5 home prem games per year and would qualify assuming they use that same criteria next year, so the only advice I can provide is go to as many games as possible