The things I normally ask people (apart from obvious stuff like names, addresses, contact details etc) are:
Marital status; if a couple are likely to marry, I write in a clause to state that the wills remain valid after marriage - otherwise, they would automatically be revoked.
Whether they have any assets outside the UK; if so, I'll advise on whether they need to make a separate will in that country to cover that property.
Whether they are a director of a limited company; if so, I'll advise on various aspects regarding those assets
Whether there is anyone who could consider themselves a dependent and therefore have a claim, such as a step child
Ask about the value of their estate and provide information and advice about inheritance tax
Ask whether they wish to specify anything about funeral wishes, such as a particular religious ceremony, organ donation, etc.
Find out whether they would like to leave a gift of personal possessions to anyone
Ditto re a specific cash gift
Talk about guardianship, and give guidance as necessary.
Even in the most straightforward scenario, ask when they'd like their children to inherit, and what they'd want to happen if one of their beneficiaries dies before them
And various other aspects depending on the individual circumstances of the client.
The disadvantage of a WH Smith form is that it can't ask you about your individual circumstances and offer tailor made advice.