For cash games tight is usually right except if everyone else is also playing tight. Then you loosen up and start getting into more pots with more marginal hands. You don't want to play recklessly but whenever you have position and you know your opponent will likely fold if he misses the flop and someone bets it's fine to see some flops with marginal hands and make some semi bluffs if you miss the flop it looks like your opponent missed too.
The thing about poker is that your cards are but a small fraction of the equation. It's not what you have that's important but what your opponent thinks you have and what you think your opponent has. It's a game of reading people first and having the best hand second.
The table you play at is also very important. If you get the feeling that you are outmatched then get up and find a new table. There is no need to struggle against superior players and lose. Find a table where the players are your level or lower and make some cash.
As for studying previous hands, you want to look for bad decisions that you made. Of course you need to know the difference between a bad decision and a good one first. This is something that will require some studying on your part. Read some poker books, watch poker training videos and post hands for discussion. Here's a short list of things to look for.
1. Was my hand within the accepted range for my position? In other words if you opened in UTG position with 67s you made a mistake. If you opened with the same hand on the button however it was solid play. Your calling range should tighter than your opening range but you also need to look at pot
odds. If someone raised and was called by say 2 other players and action falls to you it might be okay to call with 67s and see a flop. Against only one opponent who raised though its better to fold.
2. Was my bet sizing correct? You always want to open with a 3 to 4 x BB raise. After the flop you want to keep bets reasonable (50% pot or so) if you're betting for value (getting more money into the pot). If you're semi
bluffing or the flop is great for drawing hands that you don't have a piece of then make your bets bigger (75% to 150% pot size) to try and take it down or drive out drawing hands.
3. Was my play EV+ or EV-? This one can be a bit tricky at first. Sure you can just run it through an
equity analyzer but its better to understand why a play is profitable or not. To put it very simply you take the number of outs you had and multiply it by 2 if you're going to have further betting after the next card or no more cards are coming, or multiply by 4 if no further betting will be made and you still have 2 cards to come (all-in situation on the flop). So multiply by 2 for 1 card and by 4 for 2 cards. Then subtract the
pot odds (the bet you're making in relation to the size of the pot). If the result is more than 0 then it's EV+ (profitable). If it's less than 0 it's EV- (not profitable). Keep in mind that equity is a long term consideration. You can make all the correct decisions and still lose or make a bad one and win but in the long run these decisions will either lose you money or make you money.
4. Did I play the river correctly? If you has the best hand did you bet the right amount to entice a call but still add a decent amount of chips to your stack? If you were the caller, did you get the right odds to call? If you made a semi-
bluff or a cold bluff did you bet big enough to not get called?
As you can see there are so many things to consider that it's impossible to list them all in a forum post. Read some books on position, pot odds, equity and hand ranges. I can suggest "Harrington on Holdem" as a good one to start with.