If the person has prepared ("put your affairs in order") then they will have a will and an executor. And this executor will have a list of the life insurance policies and will contact the companies to arrange payouts to the beneficiaries. It's not really the beneficiary's job to do that. If the person hasn't made a list of their policies, but has a will and an executor, then the executor can try things like looking at recently paid bills (you're sending $100 a month to "Friendly Life Insurance Company"? Bet it's a life insurance policy) or paperwork that is in the person's home or their safety deposit boxes. Even if you don't have the key to those boxes, a copy of the will and the death certificate will get the box drilled out for you. If you don't know what bank they might have SD boxes at, again your paperwork will get the manager to find out for you if there is a box at that particular branch, so a day spent visiting branches can be fruitful. (Something I know from personal experience with someone whose affairs were nowhere near in order.)
Generally you find out you're a beneficiary of a will because the executor tells you. I suppose it's possible that a person might name you beneficiary of their life insurance without telling you or anyone else, and without writing a will, but it's pretty unlikely. If you're worried, I suggest you encourage your parents, grandparents, and other likely namers of you to write up some paperwork and keep it somewhere family is likely to find it. (Not hidden inside a book on a bookcase or in the back of the wool cupboard.)