I started giving mine pocket money from their 7th birthdays, when their maths could understand more about spending some / saving some / how long you would have to save to buy X, or how much you would have left if you bought Y, etc.
I used to give them money when we went to things like a Christmas Fayre, and reiterate that it was theirs and that was the finite amount. Re-explain every time they should go round all the stalls and see everything that they might want to spend it on, before using it all up on the first stall. Remind them they don't have to spend it - if they prefer, or if have some left, it is theirs to keep.
As others have said - modelling things....we have a charity shop on our High Street with a book room and they learnt early on you could get 6 or 8 books in there for the price of one at the Book fair at school, or, even better free from the library each week. Same with showing them where to buy sweets (supermarket or £ shop etc, rather than at the cinema or theatre etc.). All normal things to me, but when done with something they want, it makes sense that you can get more for your money in one place than another.
From when they were babies, I used to put any money they were given into their savings accounts as a default. Obviously as babies or toddlers they didn't have a clue, but even as they got older, birthday and Christmas they would usually have lots of presents / new toys / new clothes or whatever, so it wasn't usually a time when they needed anything else new. During the year they could have money out to buy things, but it wasn't a sort of "forced" - 'What do you want to spend your money on?' type of going to look for something to spend on, more a calmer, 'looking for the best deal on something they have really decided they want' decision.
Then, as they get older, and their 'pocket money' increases, or becomes an allowance, let them make decisions with their money about how important it is they have the fancier phone or named trainers or whatever it is they would happily spend your money on.