Ideas to finding tactics

Motiffs that makes tactical shots or Ways to decide if there’s tactics in the position.Look for:

Under defended pieces/pawns

Weak pieces or weak squares

Airy/unsafe king

Control of open files or diagonals

Queen, rook, king[any order] on same file,rank, or diagonal

Opportunities for knight forks or pins

Checks[even if they look silly]

Batteries[combinations of Q,R.B ON files,ranks, or diagonals]

Back rank weaknesses

Passed pawns on 6^th, 7^th, ranks

Positional advantages such contol of file or diagonal

Sacrificial possibilities around f2,g2,h2 or symmetical square

Is there a discovered check?

Well, such classifications have scientific value, but I have never seen anyone follow them in real life. Just can't imagine a person starting at the board: "Ok, open lines? Do I have any? Or maybe there is a discovered check? No, I guess I should pay special attention to my opponent's back rank weakness". 

No, I don't see using this as a checklist, it's still worth reading through them and thinking about them. Dan Heisman wrote an article called "The Seeds of Tactical Destruction" with a similar theme - things to think about while playing, because they might signal that there's a tactic in the position. The more often you think about these types of things, the more likely you'll notice them when playing your own games.

Far be it from me to disagree on Chess with a WGM and a NM, but at my level I do find it helpful to look for things like weak squares or undefended pieces when trying to find a tactic or strategy.  I don't have an explicit checklist that I go through before each move, but I do keep ideas like these in my head.  If I notice that my opponent has an undefended piece, I start looking for ways I can attack it.  If he pushes a pawn, or otherwise creates a weak square, I start to look for ways I can occupy it (or take advantage of it).

I've been reading Silman's "Reasses Your Chess Workbook" and in it he recommends listing the imbalances in a position when you start evaluating it.  For example, does one side have a bishop pair, while the other has a bishop and a knight?  What are the differences in development?  Pawn structure?  Material? Etc.  Once you identify where an imbalance lies, and in who's favor it is, you can begin to start looking for the best way to increase it (if it is yours) or neutralize it (if it is your opponents).

But I guess at the Master level most of this stuff comes naturally and without much conscious thought.

I generally agree on the view that "learning" chess themes doesn't make you a better tactician, but actually solving tactical puzzles (learning the real chess "language", which is calculating variations) does.

However, I have many times found myself considering positional aspects of the position when the right idea just doesn't pop up, like, "Hmm, OK, he has a weak backrank, maybe I have some trick taking advantage of that," or "black has too many undefended pieces, this problem should be about it" etc, and they help me get into the position.