Always listen to your body.........if you`re having a good day,pile it on,if not go a bit lighter.
Intensity is key......go as heavy as possible for the rep range you`re shooting for.
Heavy for 10 reps and heavy for 5 reps is still heavy for that range.
If you feel like crap,go a bit lighter but rest less between sets and incorporate some intensity techniques such as Super-Sets,Drop-Sets,Tri-Sets,etc. etc.
Combining exercises with no rest between them or resting less will make up for using lighter weights as they will feel heavier than usual.