Hi oxleyroad,
There's possibly no one size fits all answer so I will add to the smorgasbord of ideas and advice which you will encounter. I've lived with anxiety disorder most of my adult life. It started around the age of 17 and has come and gone with various levels of strength and intensity, often with no defined catalyst - I've had moments of environmental hell where my mind has been fine, and moments with no stress where I've wanted to crawl into a ball and die.
Vipassana has made a profound difference for me personally in regards to my anxiety, in that for the most part it does not affect me anymore. In the past, I've have a thought, or a somatic physical feeling, or both, and knot myself up into a ball, trying to think my way out of my fearfulness, or will it to go away, only to spiral deeper when my emotional wellbeing or feeling didn't improve. I've since learned you can't think yourself happy, and that objects may mask, but they will never cure.
So what does practice aid with?
Over time, you will identify the distinction between experiencing only what is with you in the present, and the reality you create out of your memories of the past and your fears or wants of the future. You've mentioned not being able to pick up on this, which is only natural. You have been creating your subjective interpretation of reality for decades, this is not something that disappears overnight. It is a very gradual process, I myself have been at this for a reasonable amount of time now, and it is still very easy for me to slip into my old mental algorithm, trying to remind myself of things I need to do, telling myself all the "coulda shoulda wouldas" of my past, etc etc. Sometimes I can pick up on this before it even happens, othertimes I realise I've been thinking myself in circles for minutes without noticing. This is partially where the breath comes in, not just as a concentration object, but as an involuntary constant you can always come back to. Through concentration on the breath, and just observing your mind and the emotional reactions, over time you should separate yourself from the ego that gets so very caught up in thinking and emoting.
You will come to know the practice of not thinking, because you will see the present, and only the present. There won't be any self evaluation, expectation, needs, wants, recollection, or any other brain farts that accompany most of our waking moments. But it requires time and patience.
As a general piece of advice, a lot of this is about abandoning expectations. Don't expect Nirvana. Don't expect the perfect sitting, the perfect position, the perfect attention on the perfect piece of breath. Don't expect to be happy, to be fixed, to reach some sort of defined point where you've "made it". We are all just instances in a potentially infinite reality. Life sucks, and it is beautiful, and it's traumatic and it's ice cream and sometimes its a shit sandwich. Good things come from bad, and vice versa, in the scheme of things all will pass. You can't really control most of it, so stop worrying about driving the bus and instead enjoy being a passenger.
So there you go, some tips for sitting and some amateur philosophy. I hope it may be of some use to you. If you are interested I can point you to some audio resources if you want, for my first couple of years especially I would listen to 30-60 mins of Dharma talks every morning on walks. Some of them have no benefit, some of them were the source of profound insight.