start with everything obvious, then you need to think outside the box a bit!!

even stuff like smoking, yes its banned but that dont stop folk and its a risk you can mitigate easily with no smoking policy, removing and banning some one who smokes etc.

all sorts of wierd things to think about, people with lighters on furniture, petrol bombing through civil disorder, fireworks, flares, flaming sambukas etc etc etc

A lot of things you will find no action is required as the risk is minimal or its not reasonable to take action.

Your mate know any other pub landlords?? if so look at his risk assessment. Is he part of a pub chain/franchise?? the head office may have a standardised format risk assessment you can work from and add to.