It depends on the situation, but a rough general guideline is:
Open-raise 77+ at all times from anywhere.
22-66 in 6-max: open-raise from anywhere
22-66 in full ring: limp in early position on a passive table, fold in early position on a passive table
As for calling a 3-bet: apply the 5/10 rule: if calling costs you less than 5% of your effective stack (i.e. if villain is stacked shorter than you, you need to count with his stack size as you'll never win more than that), then absolutely call.
If calling costs you between 5-10% of your effective stack, then it depends on the villain and how easily you'll think he'll pay you off if you hit (or how easily you'll be able to bluff him off his hand).
If calling costs you more than 10% of your effective stack, then fold to the 3-bet.