simply:
- use a quality wash mitt & not a sponge (save that for the sills & wheels)
- use 2 buckets; 1 for shampoo, the other clean water for regularly rinsing
- do not do it on a hot day and/ or under direct sunlight
- wash top to bottom
Use decent products (i like meguirs)
for the best (real world) results; after washing, clay bar (Until you've clay bared your car you will not know about good finish - it is an amazing product.
); decent wax (i use meg nxt); then top gloss.
btw I found the momo leathers on my old 156 never took to Autogylms leather care.