Its a frustratingly unanswerable question.
There is no universal right course to take
You might put in a low offer on a house, and the vender accepts it because they are desperate to complete their change
You might put in a very overpriced high offer in and the vendor might decline it even though its far more than reasonable.
Sometimes people have a set price they have to sell for to make up sizing possible or just some random amount that they feel the house is worth so to offer less would be an insult(which may or may not be a price based on reality or they could be deluded).
Unfortunately its just hard to judge.
If 3 identical houses were for sale
If one is priced for 400 and you offer asking price you've got a. goo deal.
If one is priced 440, and you offer at 95% of asking price you might feel you've got 20,000 off but still pay more than house a
If one was 390,000 and you offer over asking price than you still might have a deal!
And unfortunately how much a house is worth is made up of a million factors. If for example a house is up for 200 and it needs renovation works, the price you would offer would be very different if its a 250,000 house needing 25,000 of renovation or if its a 200,000 house needing 25,000 of renovation. The vendor might have already discounted it for the renovation
Where i am, houses are routinely selling over asking so what would have been the right tatic 6 months ago or even two towns away, wont be the right one here
Its very different if its the only house for sale in a village to if its competing against 10 houses on the same road (even with that are the all identical or will this one insist on more because its the only one with parking)
I offered reasonably on a house that was declined, that house is still for sale a year later and the vendor is declining similar offers because they are happy to wait for the right amount to come
Often on mumsnet you here people say they wouldn't negotiate/entertakn further offers if offended but as long as its within 10% of price then most reasonable vendors won't refuse to enter into negotiation (even if its just to say asking price only)