how to improve in SPOTTING tactics??

@blueemu  it's not necessary that they should blunder . In top level matches there are a lot of tactics in lots of matches that doesn't means they are blundering alot at this high level!

Note that some engines have a "tactics solving" mode where they deeply explore sacrifices, but this mode is not really used during normal games.

Meaning that even engines (who play objectively better) do not focus on recognizing tactics, they just check some tactical moves and when they do not see any advantage, they explore different branches. In conclusion, "searching for tactics" should be done very shallowly.

The exception comes when there could be a tactics, but probably unsound (e.g. scarifices on h7). In that case, you should check for tactics there every half-move.

If a winning tactic exists, then the opponent has already blundered.

Are you under the weird impression that winning tactics can be found in equal positions? If one side has a winning tactic, then they ALREADY have a won position... by definition.