Like anything really, haggle.
Keep offering a price until the Agent etc or house owner says ok.
Don't forget you get price even lower due probs found in building survey.
I bought a student house, £150K, I offered 135K, 139K, then 142K and sold-it was in an ok area but easily snapped up by other buyers-I lost out twice in the same street.
Servey show damp kitchen, fear on tv about price crashes. I knocked it down to 137K and they agreed.
Cost me £3K in parts for me and Dad to rebuild everything and was valued at £180K last year probably 170K now and probably get £155K offers but I wouldn;t less than 160K.
Some add 10% etc.
I think you should start at 160K at least and up you go till both sides are happy.
My pal offered 40K less for £200k house 2 yrs ago and sold on first offer but it is a flood risk area lol.