Never let runs of bad cards influence your decision to play a hand. A hand either has equity to play, or it doesn't.
These aren't the "key situations" you're looking for. Throwing chips in with easily dominated hands. While that 10-J spades may look great from the button, if you have a raise and a call in front of you, tons of hands are way ahead 10-10, J-J, Q-Q, K-K, A-A, 10-Q, 10-K, 10-A, J-Q, J-K, J-A. Lots of others besides these that are 60/40 favorites against you.
Putting chips in dominated is very bad, situations where you have only a 30% chance of winning or less.
Set ranges for opening a pot. From early position play only strong hands, 99-AA including AK AQ.
As your position gets stronger, from middle and late position, you can open your range more.
Again these are pots that you are the first one to make a bet. Don't limp in if you are first to act. Raise or fold.
Don't vary your opening bet based on your hand strength or position, come in the same with every hand you play, 3 or 4 bbs, whatever is the norm at the game. Makes it very difficult for opponents to figure out what you have this way.
When your not playing in a hand, try to figure out what hand the continuing players may hold, or a range.
Make notes on players as you learn what they do. Many players will bet big with AA or KK pre, but bet smaller with weaker hands. Some will do the opposite.
The best position you can bluff from is the button, when everyone else folds to you, just come in the same way 3x the bb. The type of player that is in the sb and bb will also influence your decision to continue if called. Is this a call with any cards guy? Or a tighter player?
More times then not, unless your opponent holds a big hand, or a good draw, after the flop is checked to you, a continuation bet will take it down. How well this works depends on your style of play.
If your calling every hand and playing loose because your bored, attentive players will pick up on this, and will be able to get you in bad situations. If your playing a solid game, they will be less likely to call you down.
To avoid getting bored, watch the other players tendencies, are they loose cannons, passive tight, calling stations, solid TAG players, NIT's? What range are they opening with?