Hello
Everyone has their favourites, stand by to get three dozen completely different answers from people who say theirs is the only way to do it!
I use different mixes for different uses.
For seed sowing I buy the cheapest supermarket bagged compost I can find (Lidl usually) & then sieve it. (Main thing for seeds is this should be sterile. Low nutrients so you need to transplant fairly soon but cheap and easy.)
For most other uses I use equal amounts of soil, coir and home made compost from the compost heap. My soil is quite gritty. You might need some sharp sand if yours isn't.
For heavy feeders or things that will be in pots a long time & put a layer of composted straw and cow manure in the bottom of the container for the roots to grow down into.
Its astonishing how leafmould disappears however much you think you're starting with. I never have enough leaves to make more than a dirty bottom in the container I collect them in by the time they rot down!
I buy solid coir blocks from Amazon.
Looking on with interest to see what everyone else does...
Windy