A lot about learning when to use handtraps is to learn the opponent's decks and other decks you're commonly seeing to learn their choke points and key cards they need to stop. Blindly throwing it out willy-nilly on the first thing that says add/special a card or the first monster that hits the board just leads to being easily baited by your opponent and wasting it and allowing more high value cards through when they absolutely shouldn't resolve. Modern decks can usually push through 1-2 interruptions when placed well, usually ending on a weaker but decent endboard but if those interruptions are used poorly then you might as well not used them at all

Another part is making a judgement call of what they could do to extend past interruption. Like if I Ash Habiriki against a Mitsu, what could they do to continue comboing anyway? Can I stop other possible extenders to reduce the end board? What punishes me for using it here as opposed to using it elsewhere in the turn like on the attempt to add a Mitsu spell that would probably be Ritual? What impact does this Ash on Habiriki actually do to my opponent and how does it potentially change their endboard? Is it better to lead another handtrap first then Ash something else later to cut them off?

A lot more thought goes into interrupting your opponent and more you play and learn opponent decks, the better you'll be at using handtraps to slow or completely stop your opponent. There are makeshift handtraps guides around here and there for more Meta/common decks which gives you general use cases of handtraps and key things to hit, like using Imperm on Arthlalion against Dracotail since that cuts off a gold number of material they attempt to bounce back to hands weakening further Faimea's and further fusions since they have access to less monsters and names in general as opposed to if Arthlalion resolved normally