its not just about the right now odds the bigger calculation is implied odds. you need to look at what the opponent has for a stack after that bet. you need to calculate how much you think you can extract from him if you hit your hand.
i will try to go through a hand and thought process so bare with me.
you are dealt 8h,9h and blinds are 25-50 and you have 1850 in chips.
you are up against one opponent whos has 2200and you have position.
pre flop he raises to 150 (standard raise) and you call.
the flop comes 6s,7d,kh. opponent bets 150.
Step one-open ended gut shot is 33%, he bet 150 into 375 so pot odds are 2.5-1 if you only follow right now odds you should fold. but now pot odds come in. first thing you need to do is put your opponent on a range of
hands based on his tendancies. lets say for calculation purposes we put him on AK,KQ,KJ,66,77, or kk because of his preflop raise all of those hands we can beat if we hit our straight and i would say all of but KJ we would get all his chips. so at 2.5-1 real odds were not getting the right price, but at 150 for 1700 or 11-1 (which is what we have left) we are getting the odds to call so the correct play would be to call the bet (based on the hands we put him on i dont think re-raising is a good play because he will ussally re-raise with 4 out of the 6 hands making a tough discision for all our chips).
Their are other exceptions like if we dont think we will get paid off if we hit. you also need to look at how much they typically bet per round throuhout a hand and that way when you play against them in a hand you know exactly what their bets will be in relation to the pot.
its a tough subject to explain because it has so many varriables but some advice would be:
1- Always see how much they have in their stack to see if chasing the draw can warrent a call or raise
2- With high percentage draws like flush, open ended straight and combination flush/straight draws re-raising is ussally a better play because by raising you have to ways to win the pot by them folding or by you hitting your hand. if you dont re-raise those draws you can only win one way by having the best hand. you want to calculate the re-raise based on what you come up with for a range of hands. because like i said in the one above re-raise is probly not your best option.
Good luck and I hope this helped.