Aallon's quick & simple soil mix
A quick and easy soil mix would require:
5 parts soil. Normal commercial potting soil should be fine.
5 parts perlite. This enhances aeration of the soil-mix, helps prevent over-watering by increasing drainage and reduces soil compaction. Perlite can be replaced with coarse vermiculite or crushed expanded clay balls (mica, leca, geolite).
2 parts composted organic matter. This can be normal household compost. If you can find composted worm castings, seaweed or composted manures (chicken, horse) they can also be used for extra kick. Non-composted manures make the soil-mix too 'hot' for the plants and should be avoided.