First, be sure to have a good look outside. Don't just look at the house, but see how much driveway it has, how much front garden, and what access is like: for instance is it possible to get through directly to the rear of the property (think security risk) or is it gated etc?
Look at the adjacent properties and those across the road: do they all look occupied? Does it look like the owners are taking care of their properties? All these things can help you to form an impression of the area before going inside. Because the danger is that people focus purely on the house itself when buying a house does not just get you a plot of land that floats in space: you have to get to that house, live in it, which means driving down the road each day and also putting up with whatever the other owners in the road are up to: so it is as important to get a feel for those sorts of things too.
Therefore if the property you are looking at is on a road you think might get busy, it is worth taking a drive past it at rush hour too in the morning and evening to see if it would be hard to get in or out of the property due to the volume of traffic. Also if you are seriously considering a particular property and this is not your first viewing, then seriously consider driving round at night too just to see that everything is OK (eg that nice looking pub across the road during the day isn't blaring out really loud music at night!)
Now, when it comes to viewing the property itself, you should have your checklist with you (see other articles) that contains the elements you desire in a home so you can note how it performs against each of those. You might also consider taking a tape measure around with you if there are particular measurements you want to take (eg length of front garden or width of driveway to see if you can easily fit two cars) and so on.
When going around the house, a key tip is not to get too bogged down in what the current furnishings and decoration is like. Naturally these are important and visual elements but they are also easily changed, so don't focus on those too much: after all chances are that when you get in you'll change all of those anyway, so instead focus on important things like layout, space, looking for cracks and that sort of thing. Do wander where you like: if the estate agent seems to be glossing over a particular room or more keen on showing yourself one thing over another don't get rushed and find out what you need to know!
More first-time house buying articles: