Guidance on how to start your writing up

It is NOT a good idea to start by summarising your viewpoint, e.g. 'I think it would be a good idea to ban advertising of sweets because...'

This is not likely to lead to a good answer because you will tend to go on to only write things that back up your judgement. What about the arguments against?

It IS a good idea to start by identifying all the stakeholders who might be affected by a ban.

This is a useful place to start because it helps to present a view of the whole picture. It also gives you a set of stakeholders you can go on to write about.