DIY potting compost

Unashamedly borrowed from a Gardener's World article :-

How to make your own peat-free compost
It’s also easy to make your own peat-free potting mix, using a mix of different ingredients, including well-rotted leaf mould, garden compost, vermiculite and garden soil. Monty Don recommends a mix of three parts coir, one part sieved garden compost, one part sieved loam and one part sharp sand, perlite or horticultural grit. Find out more about the some of the ingredients used to make peat-free composts, below:
Leaf mould – An excellent soil conditioner and easy to make yourself. If you have lots of leaves, try making a leaf mould bin to process large amounts, or on a smaller scale you can use plastic sacks.
Home-made garden compost –  Every garden should be able to produce this and the key is balancing green, leafy nitrogen-rich material with carbon-rich brown material, like woody stems and cardboard. 
Loam – Essentially garden soil, you can buy good quality loam (or topsoil) from the garden centre. Alternatively you can use old sections of turf, which you stack up, grass side down, and cover with tarpaulin. After around a year it will have broken down into good, loamy soil, which you can use in potting mixes.
Coir – A waste product from coconut plantations in tropical countries like India and Sri Lanka, you’ll often come across it in compressed blocks that expand when watered. It’s absorbent and an excellent open growing medium for sowing seeds and growing plants.