Loosen up, but not too much. Against some guys I will value bet 2ndPGK. If they catch it... reload. You'll get them sooner or later.
If someone calls down With highcards - obviously you should loosen up. I think where I see many fellow players go wrong is that they have this weired idea that these guys don't deserve to win any pot, and they keep betting AK high all the way to the river, and when bottom pair calls they scream bloody murder.
Obviously you don't want to semi bluff... or make any kind of bluff.
Also be careful that the betting/raising range of a calling station might be much tighter than their calling down with trash suggests. So bet into them, don't call them unless you see that their raising range is way out there, too.