Im by no means an excellent coach but here is my general thought process for doubling.
First, I never "always" double two players that are on the court at the same time. Sometimes coaches will have one big time PER starter and another on Bench and generally only sub for each other. In this instance I may double both but if there is a high likelihood theyre on the court at the same time for any significant amount, I dont. (I believe some coaches will "always" double two players generally with the caveat they dont play next to each other)
Also, I really dont like the double two guys "if leading scorer" approach. In fact I dont use If leading scorer *almost* ever.
Then I look at volume, generally I use the shorthand OFF% in the player gameplan page. I dont have a cutoff per se but am generally looking for something around 18% or above, give or take and relative to teammates. Next I'll look for efficiency, Point per Possession (efficiency), Points per Minute (volume...kept on a spreadsheet I use) if the high volume guy is also very efficient, and just as important, significantly more efficiency than his teammates (or most of them) hes probably getting a double.
I also make exceptions where the guys is, say the 2nd or 3rd scorer but only perimeter threat I may double.
I compare quality of defender (man) or group (zone), If I feel I can defend him well without it, I dont.
Against FB team especially, I look at what % of their points come from the FT line, I'll admit though, I get lazy and skip this step often. But if a lot of his points are from the stripe, Im less likely to double.
Finally, the Key for me is, If I "always" double a player, I essentially do a quick recalc of the teams 3pt attempt rate and adjust team defense without that players attempts in both numerator and denominator. Ex: If 40% of a teams shots are 3s I may play +1 or +2, but if i decide to double a player and that number drops to 25%, Id use a double, and -1 or -2. On occasion I get very extreme with this as well (double, -5) etc.
It sounds like a lot but when life gets in the way I can generally gameplan in like 5 min. Hope this helps, interested in others thoughts as well.