IMO, and it has been said before, depends on your position, but if you are intending on playing low-mid PPs and want a good strategy, one that I find that works is to have a set betting pattern that makes you feel comfortable(one your willing to lose sometime, but at the same time, one that makes others think you have a marginal hand).
In order for this to work you have to set yourself with an image of a TAG player and the "comfortable bet"(CB, which I like to call it) has to be a bet your willing to use for every hand(you decide to play) regardless of the strength of your hand. Why the same bet?, you may ask, and the answer is simple, "consealment".
This strategy may be hard to play at all times, but at the right table it works perfectly.
Now back to OP using the strategy described above: Say you have 33 in EP and make the CB, [and on the right table(TAG preferably) you may get a few callers but not too many raisers unless they have monsters, which you can fold to any aggressive, solid TAG players], the flop comes 3Q7 rainbow, now because of your preflop bet(say 3xBB) most players will put you on high cards or a strong PP but not a low PP because you had bet OOP (because you have set yourself up as a TAG player ealier in the game, and a solid TAG player doesn't open betting preflop OOP unless he has something good and only checks low to mid PP OOP), now you will feel safe to check/raise, hoping someone has hit the board(dont worry too much about another player hitting a set, as Phil Gordon has mentioned in his "Little Green Book", the chance of set over set happens 1 in 100 times) and bets, and this is where you can again check or raise because the only cards beating you now are QQ,77. If the turn comes out one of the suited cards in the flop make the chaser pay for his draw.
IMO, this hand is a no brainer and there are definately flaws in the way I play my PPs and most on this forum will disagree with me and I'm fine with it, but my point is , do not limp with low to mid PP when in position and if on a TAG table and feel you have a good read on your opponents then bet those PPs because when you hit your set they will pay you off nicely and if you don't hit your set then it's an easy fold or steal depending on your reads on the table.