To come to the UK as a general visitor, you must be able to show that:
you are 18 or over;
you intend to visit the UK for no more than 6 months (or 12 months if you are coming with an academic visitor);
you intend to leave the UK at the end of your visit;
you have enough money to support and accommodate yourself without working or help from public funds, or you and any dependants will be supported and accommodated by relatives or friends;
you can meet the cost of the return or onward journey; and
you are not in transit to a country outside the 'Common Travel Area' (Ireland, the UK, the Isle of Man and the Channel Islands).
You must also be able to show that, during your visit, you do not intend to:
take paid or unpaid employment, produce goods or provide services, including the selling of goods or services directly to members of the public;
do a course of study, as long as this study is not the main reason for your visit (see the General visitors page for 'permitted study');
marry or register a civil partnership, or give notice of marriage or civil partnership;
carry out the activities of a business visitor, a sports visitor or an entertainer visitor; or
receive private medical treatment.
I'd call them if you're unsure about anything.
It's all standard visa stuff, basically you need an onward flight, don't work, have enough money to support yourself and leave before 6 months. The only different bit about it is the biometric appointment, but he might not even need that (check the exempt list).
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