When to offer
Once you decide on a particular property, make an offer as soon as possible to the agent and confirm in writing, copying in your solicitor. Make it clear that the offer is 'subject to contract and survey' - meaning you can still pull out if anything serious is highlighted in a subsequent survey (see Getting a Survey). Do not sign anything at this stage without legal advice.

How much?
The level of your offer will of course depend on how much you can afford (see What's Your Budget) but you should have been looking at properties within your budget, anyway.
Ask the agent for any background history. How long has the property been on the market? Have there been any other offers? If there have, why did they fall through? This can help decide the level of the offer.

Consider the market
If it's a seller's market, don't waste time offering below the asking price unless you know the owner is getting desperate to sell. Make sure you know why it hasn't sold already - and be ready to live with those reasons.

If the market is slow, consider making an offer below the asking price - a good estate agent should be able to advise. Although they stand to make less commission, they risk making no commission at all if you don't offer.

Consider making a lower offer if you're a serious buyer who can move quickly: a first-time buyer with a mortgage approved in principal, for example, or a cash buyer. It could swing the seller in your favour, even if they've had a higher offer.