Hello, i´ve done 2 or 3 renders with 3 point key setup, and they always end up a little too dark.
When doing this type of renders i have seen people set world environment color to pure black, beacause this also makes the scene tend to gray.
but considering studio photoshooting exists in a real environment, putting an HDRi environment is a good aproach or should i use ambient occlusion as someone suggested?
Either way, i have this overall darkness all the time...
Ambient occlusion is going to further darken your scene if you use it as a "multiply", which is normal. But yes, adding an HDRi environment will flood your render with realistic fill light - because reality rarely has a pure black fill, unless in a completely blacked-out room.
Also, have you tried increasing your lights' intensity?