Generally People tend to go to phone shops such as; Carphone Warehouse, or a network provider shop.
If you go into a store, you may get a bunch of phones on desk to try out or a plastic model of the actual phone so people can get a taste of what they are like before actually buying.
But If you are lucky enough, there may be a sales assistant free to give you advice on the perfect one to suit you.
They may even give you advice on how to set it up and how to transfer stuff from your old phone to your new one.
Most stores ask you if you want to take warranty out on them. We would advise you do depending on what kind of phone you are getting. If you do then it’s up to you, but it costs extra for it and remember to ask what it covers and what it doesn’t.