I don't know how to "deal" with flashbacks....There are lots of good grounding techniques, like providing yourself with strong sensory material linked to the present...for example if your flashback is a smell, counteract it by smelling something strong (ie: coffee grounds), that sort of thing...fortunately I have had mild flashbacks, not directly reliving trauma. I have only been able to hang on and get through them...somehow "dealing with" them implies a control that I never had.

As for dealing with triggers, I am learning how to do this one. The best thing that I can do is to get ahead of the trigger, before the negative emotion comes up...to be able to recognize that something around me is stirring up feelings from the past, to identify the past event, and to contrast that very strongly with what is really going on around me.

For example, the sound of children playing in the courtyard late at night brought up feelings, an immediate thought that their parents were being careless and neglectful, ominous feelings of portending danger, and anger on my part, and then realizing that was a trigger to my own childhood experience. I then extended that realization to imagining that the children in the courtyard were staying up late playing, closely supervised by their parents, having a family party for some good reason, that they were safe and happy, and that is the meaning of what I was hearing....and voila! End of the trigger.......

As for more persistent triggers, personalities that resemble my abusers that I deal with IRL, I have to practice good boundaries, add in tools like anger or positive reinforcement when needed, try to focus on the differences between these people and the abusers that I am projecting onto them.

Always, I think, the key is to recognize that today is different from the past. We are safer, we have more control, and generally the people/situations that we encounter are not the same, even if they evoke similar feelings.