Players Decide, PCs act.

You tell me what your PC wants to achieve and how. I set the DC to check how well they perform at that attempt (or declare "no roll needed", because it's trivial / impossible).

You want to persuade an NPC? Tell me the gist of your argument and I'll consider how receptive your target is and set a DC for checking how well your PC can present said argument.

(In some cases like "I want to hit them real good with my sword" or "I want to climb up that wall", no detailed description is necessary, we both know what you mean.)