There are four main ways to arrive into the United Kingdom. By air, by sea, by land across the border from the Republic of Ireland , or by train, through the Channel Tunnel.
By air is much the same as any westernised nation, and all the major airports are efficient, clean, and well organised. They have good links to the cities they serve, and most provide a good choice of airport hotels, currency exchange, and other services. Be aware that both London Heathrow and Gatwick have more than one terminal (five in the case of Heathrow), so if you are being met, and when you are heading back to depart, you need to know which terminal you will travel through. There is some distance between them, and it can take half an hour or more to change if you get it wrong.
If you are arriving by sea, the customs and immigration procedures are much the same. If you're travelling as a foot passenger on a ferry, a cruise ship passenger or using the Eurostar trains through the Channel Tunnel, the process will eventually deliver you to the arrivals hall, just as at the airport. If you are coming on the car ferry with a vehicle you will need to ensure you also have all papers for the vehicle too, and that it conforms to British regulations. You also need to ensure you do not have in excess of the permitted amounts of restricted or taxable items.
These limits and regulations are reviewed regularly, so it is advisable to check the most up to date information with the official UK Border Agency site which includes allowances, regulations, applications and requirements regarding visa's, and just about anything you would need to know.