Level 0) "I can has two cards. Diamonds are a girl's best friends. I call".
I had one at my table once who would play pocket deuces to the river, no matter what. Another one played any Tc because it was his "lucky" card. Don't ask me to explain it, because I can't.
Level 1) Here, the player begins to consider hand strength and position. Knows that AK is worth a raise UTG, and that QJ-off is a fold, but could be worth a raise from back row positions. Better than a Level 0 drooler.
Level 0 and Level 1 thinkers aren't really playing poker. It's more like group Solitaire. Level 1 thinkers might do OK, playing a slightly +EV or break even game, especially with regulars who are still stuck at Level 0. They won't win nearly as much as they could, and won't last against stiff competition.
Level 2) Thinks about own hand strength, and thinks about opponent's hand strength and how his hand stacks up. Tries to get lines on opponents' play, read tells
, discern meanings behind bet sizing.
Level 3) Thinks about own hand strength, opponent's hand strength, and thinks about what opponent thinks about player's hand strength. Once you reach this level, you can set traps, set up bluffs, make correct hero calls and hero folds.
You want to figure out where your opponents are thinking, and stay one step ahead. You don't want to play a Level 3 game against a Level 1 opponent, as that's a good way to value own yourself. You never want to get into a situation where you outsmart yourself.
As for everything else mentioned, you definitely take all that into consideration, as well as other factors: effective stack sizes, stack-to-pot ratios, whether you want to play a big pot, or would prefer to keep it small, deep stack protection.
As for the implementation, it can't be explained in a forum post, nor can it be learned by anything short of getting in there and playing and practicing, and study: reading material as well as post game analysis. You can bring your tough situations here to get some other opinions and outside analysis.