This is a million-dollar question for every buyer!
I use a method called Comparative Market Analysis, or CMA. I pick 2-3 similar properties sold within half a mile of the subject property in the past 6 months to use as comparables, or comps. No two properties on the market that are exactly the same, so we have to make some adjustments. These adjustments are based on location, property type, square footage, distance to public transit, parking, deck, patio, renovation quality, projected appreciation, finished basement, etc. I come up with the value for these comps if they had the exact same features as the subject property. Then I take the average of the adjusted numbers of the comps to come up with the range of estimated market value.
The best way to figure out the best price to offer is to look at the CMA as an objective report and ignore the list price. Both consumers and some real estate agents can have anchoring bias. If the home is priced too high, even if you get it 50k below list price, it doesn't necessarily mean you are getting a good deal.