Optimising my flush (or straight) draw payoffs (NLTRN)

[aaaaa]

In a NL HU game, how much do I bet to induce a call when my flush card actually hits on the turn? I notice most opponents fold on my bets. This is the 10$ game on Full Tilt.

A typical scenario is this:

Usually the pot size gets to be 300 chips (in a 1500 NLHU game) and the blinds are 15/30.
My cards:
7h 8h (some mid-suited connectors. So I double or triple the BB)

FLOP: Kh 10h 7s (some high cards. Paired the low card, so I bet 70% - 120% of the pot)

TURN: 4h (FLUSH hits here, NOW WHAT??)

The villian is playing (calling) like he has a pair, probably K or 10.

Usually I'll raise pre-flop, and then bet the pot on the flush as a semi-bluff. The pot size is thus 4-5 times the BB.

BACKGROUND --
I'm LAG (double pre-flop 60%-70% of the time, triple pre-flop 5-10%). Usually a bet 3/4th of the pot makes the opponent fold -- and this is one of my standard strategies to bluff an opponent out when I do NOT have the flush.

Is there anything I need to change drastically so my payoff in these sweet hands goes much higher?

thanks

[ChicagoRy]

If he's not giving your image action and you are really playing this laggy then you should just be able to run him over and not be concerned about your flush draw.

If your image is too nice to be called here, start cont. betting everything, and just do the same here, when it hits on the turn, check like you are weak and you'll be called a lot weaker on the river, maybe that top pair will turn into two and you can even get a raise at this level.

[MFpoker]

i like to push to make it look like a really fishy bluff. top pair calls a lot there.