If I think my opponent has a hand he might fold, I'll usually bet or raise with them. Depends on how your opponent plays. Also, if you are drawing to them you can keep in mind other draws on the board or scare cards that you can also bluff with if you miss your straight but one of those other cards come. Lately though online it seems the chips get so shallow so fast these types of plays just turn into all-in semi-bluffs.