Harry, Everyone has a different approach but my point is to avoid( wherever possible) fillers which contain absorbent fillers like chalk or slate dust, sawdust, flour and general rubbish. They simply blot up oils and cutting fluids and so on.
So I fill the worst 'holes' with something that is dead hard and knock the worst off with a bastard file or a flexible car body dreadnought one. Then I smear a thin coat of a concoction of filler and hard resin and rough it down to what I think is Level. Then I spray the undercoats on. Then comes the most important thing- a mist coat of a contrasting colour. Sort of the end of a spray can. So this mist coat is rubbed down until the whole thing looks like camouflage. So the hollows can be seen but leaving most of the undercoat in tact. I then fill the hollows/depressions as well as I can and add another couple of coats of undercoat- and another mist coat which is rubbed off. Then there a point when all the work is smooth enough until all the undercoat is matt finish. Then goes on the finish in two coats at a time and rubbed down to a matt finish again. At some happy point, it is time to water the workshop floor and chuck the family, the dog and the neighbour's cat out- and finish off.
OK, I was well trained- a student of the old school.
Thinks, I drove my Missus's best Audi A4 Avant S line- into a thorn bush which grew up as if by magic in front of me.
It's silver- no, the car- and it is clear over base- as well.
Cheers
N