After you have flopped a draw and decided how strong it is, you now need to consider how to play it. There are a number of factors you will need to consider before you make your decision:
The pre-flop action: Were you the aggressor pre-flop? Have you already demonstrated to the table that you like your hand? If so, then you can often continue with the pre-flop aggression, giving you the option to win the pot straight away, or building the pot even bigger for when you hit your draw. If you only called pre-flop then you should probably call. You can then keep the pot relatively small until you have hit your draw.
The number of opponents you face: Betting when you have only a draw is essentially a semi-bluff. You do not mind if you are called, but you will also be happy if your opponents fold. As with any semi-bluff, it is easier to convince only one opponent that your hand is strong than it is to convince many. The larger the number of opponents the tighter you should play your draws. Semi bluffs are less likely to work.