evaluating draws one or two streets at a time?

[thegoingoforit]

This is probably a noob question but here goes. I was wondering if it's better to evaluate odds for draws one or two streets at a time. For instance, say I flop a flush draw so I'm about 2-1 to make it by the river, but I'm
4.2-1 to make it on the turn and 4.1-1 to make it on the river if I miss the turn. So not only in terms of pot odds for calling but in terms of raising for equity, should I raise on the post-flop betting if I'm getting better than 2-1 or should I only raise based on my 4.2-1 odds to make it by the turn therefore only raising if im getting better than 4.2-1 ?

[SplawnDarts]

One, with appropriate implied odds adjustments, if you're not all in.

Two is obviously appropriate if you'll be all in.