Trial and Error! I like booking booking my younger fighters against eachother for a few matches, booking national or world caliber against accomplish or high level fighters in their same martial art, eventually expanding from the martial art (boxing) to now strikers, and if they want to go to the ground in any of those fights then I'll look for a similar striker (kung fu) to go against (boxer), Ive now used Tags to seperate my fighters once I see a few fights from them to help with this, unless I see them going out of their art I wouldn't match them with a complete martial artist until then, then they get the martial artist tag and the protective booking is up.
I also tried the whole weight class per card but it gave away for the freedom so now I'm doing 5 weight class with 1 match per weight class on the main card, then either 5 or 10 on prelims of either 1 or 2 matches per weight class, all being even.
Usually stacking with 100 characters in each class if i'm planning for 15 match cards weekly as UFC has been killing it this year 2020.
Also playing London Verse in '89 so I'm usually building the stars from their first fights and those who cant swim with their own arts will sink before they get to the test