Easy steps to happiness!
1. strip off topsoil
2. lay drains to outfall, min 800mm down
3. lay a geotextile membrane over area and down and up drainage channels
4. Backfill with compacted stone in 100-200mm layers or road planeings, do not use mixed grade type 1, as this will end up mushy. 6F2 or crushed brick will also free drain. Your stone layer should be level with the surrounding ground, but needs to be min 300mm thick for footfall or animals, thicker again if for vehicles
if you need any other help, just PM me