You did not specify if you play ring games or Sngs, and whether you play limit or no limit

For ring games you have to follow pots odds (and implied odds).
On an unpaired board you have 9 clean outs
about 18% to hit by the next card
about 35% to hit by the next two cards.

So if you have a flush draw on the flop and you think you will be raised again after the turn you need to call if you have to put in the pot <18% of it.

In Sngs only chase draws if you can do it for cheap, dont risk a major part of your stack chasing