How can i prevent this from happening

these are 2 hand histories that happened to me in a 2 hour session of 12nl holdem did i play this right or did i get sucked out by a donk.

http://www.pokerhand.org/index.php?p...ew&hand=190060
i also had another hand like this where i had pocket Q's and flopped a set of Queens and a guy had a flush draw on the flop with ace jack so i bet the pot which was like 30 bucks and he called and caught his flush on the turn but i didnt know he was on a flush draw so i kept betting into him. well i ended up losing like 90 bucks.

This JJ hand I see - you bet weak on the flop ($8 into about an $18-$20 pot) - why?
There's an obvious straight draw on the board - someone's a bit donkish for chasing the obvious draw that is not likely to be paid off - but in this case you bet less than half the pot - that looks to me like you have missed overs, a pocket pair lower than the top card showing, etc.

On the turn the guy min-bets at you. Either he has a monster already, or more likely he is testing the waters with you, still thinking you are on missed overs or a weak hand. The minute I saw his $2 bet here on the turn I'm thinking the guy has 89s. He has a pair and the straight draw and thinks you are bluffing him so he's willing to call it down here thinking his hand might be best and if not he's got outs.

So the problems I see here -
(1) weak bet on the flop - don't F around with a set on this board - there's a straight and flush draw that you are pretty much giving odds to - if you want to do that, fine - but be willing to lay the hand down when either one hits
(2) The turn big raise is good but it looks fishy after the weak flop bet - which is I suspect more why he called than that he was chasing - I mean you're reraising when a 3h shows up on the turn? Not particularly a scary card.
(3) Calling the river here - I'm not sure that this is a mistake - he could have missed the flush draw. Though in that case he's probably not value betting 1/3 or the pot - he's probably betting 3/4 to pot to chase you off. It is good that you just called here and did not reraise.