The answer is, you don't. That's why you hire professionals to do things for you. You ask others to help you and you do your research.
Life has been a lot more complicated for people recently around the world, dealing with Covid-19 and restrictions with new ways of doing things have to be found. There will inevitably be delays and last minute changes of plan, additional expenses and a lot of inconvenience. Then just when you think it's all settled and there is now an established way of doing things, it all changes again.
However, more often than not, you end up finding out things you don't know about that you need to know. I find the best way of dealing with things is to say at the beginning that I have no idea how anything works, what you want from me and in what order you want it done, so please start at the beginning and explain it to me. There always seems to be an assumption you've a) done this before and b) if you have done it before it will have been done the same way.
Here's a list of things I didn't know I had to know over recent months.
I didn't know that I'm supposed to know that:
I have to be at a hospital 2 hours prior to appointment time.
Not all medical appointments are direct billing and even if you ask if it's pay and claim or direct billing, you need to know that what you're told over the phone will differ from what actually happens on the day.
If you want to close a bank account and to actually have the account closed that you need to know that you have to ask for a clearance certificate or your bank account just remains open with a zero balance.
To ensure a smooth and swift delivery of your personal belongings via a shipping line that you need to know to ask the company you have the contract with to ask for the Bill of Lading from the Shipping company then know that although they've asked, they may not have received it and you have to know this, then you have to know that even when they give it to the shipping company that you need to know the person to contact in the UK to ask them to ensure they notify them, then you need to know they won't automatically inform your UK agent to arrange collection of your furniture for delivery to you. You also need to know that no one actually cares or accepts responsibility.
Estate agents won't date photos, evidencing damage, automatically before submitting them to the Deposit Protection Scheme, but you don't know you need to ask them to do that until after the claim has been refused, due to insufficient evidence that those photos were taken during the tenancy and not years earlier or later.
I automatically know I have to collect a ticket once I've decided what category my question/complaint fits into, then know which part of the building to go to for the corresponding ticket window.
I know that I have to do things in a certain order and ask my questions in the correct order or I'll have to take a new ticket and queue all over again.
I know where each department is and fully understand the orders barked at me to follow without being given time to process and to think about what else I don't know, that I may need to know before leaving the department and navigating my way to another building armed only with a ticket number.
Things that I do know though.
People will lie. Say things to get your business.
People and companies will fail to take ownership of their mistakes and will stop replying to emails, ignore your calls and eventually block your number.
People and companies will make things as difficult as possible for you to get refunds/monies owed in the hope you'll just go away.
People who don't know that they need to know, don't tend to understand your situation.