Im trying to become a tight aggressive player...but the biggest problem I am having is that I feel like I must make a pot size bet on the flop. Example...with BB at 30 I raised to 100 with JJ in middle possition. The next two players called and every1 else folded. The flop was 7 9 K rainbow. I was 1st to bet so i led out(trying to keep my tight aggressive image) with a pot size bet. Next guy folded and the other guy reraised. I felt he would only do that with a King. I folded. The problem is that it was like the 3rd hand and I had lost 400 in chips. What should I do differently? My biggests problem is that I feel like I have to bet the flop whether i have AK or 10s. My other question is when to play AJ or AQ...these hands seem to get me in trouble. And is it ok to limp in early possition with small pocket pairs or hands like KJ, K10, QJ? I feel like when I fold these hands and raise 4 or 5xBB with good hands I mostly pick up the blinds and I'm always behind at bubble time or way behind at final table with 18 and 27 player S&G. Thanks

You don't need to make a pot size continuation bet, you can always make it 2/3rds and save yourself some chips when they do have something. Size of the bet should also depend on board texture a dry board it doesn't need to be big.

In early position just fold hands like K10, QJ you can raise them in late position. It's ok to limp small pp early on in MTTs it depends on stack sizes relative to BB

There's nothing wrong with checking JJ on the flop when an over hits either. Granted, you won't get the same type of information that you would with a bet, but it's possible that it will check around.

More often than not, you're going to want to find out where you're at with a bet though.

You should adjust your betsize based on the size of the board and your position.

1) if you are OOP, bet large ... in position, bet smaller
This is because your range for betting OOP is tighter, so you will want to bet more in order to maximise value and reduce your opponents pot/implied odds (for the times you have a big hand). OTOH I would bet less in position.

2) if the board is wet (drawy) bet large ... on a dry board, bet smaller
You will want to bluff a lot at dry boards, because your opponent rarely has anything. If the board is K72 then they either have nothing and will fold to half or full pot, or if they have something marginal like A7 they will call either bet on the flop anyway (it's actually better against A7 to bluff small on the flop and then fire again small on the turn, than to pot flop)

Personally I only ever bet full pot when OOP on very drawy boards eg KQJ or something. I think betting pot in position makes your bluffs too expensive, and bloats the pot early which reduces your positional advantage on later streets (you are closer to allin).

also I would add the following:

too often new players worry about betting enough to fold out draws, because someone hits a flush vs their AA and they are scared itll happen again

the fact of the matter is that if he has a draw, he's not folding to a PSB anyway, so all you do is slightly reduce his implied odds , the difference in EV to you is just the little extra he calls when he chases and misses.

but if he has a marginal made hand, then a PSB is terrible for you, because if he does have such a hand, he can call many bets to showdown whether he hits or not, so its really important to get him to put his money in, especially since his equity is likely to be terrible (eg you have have him dominated with TP better kicker and he has 3 outs)

If you keep trying to bet big to push out draws, you will get called by the draws anyway, and just push out worse made hands that could have paid you off massively.