Must or Have to
The key difference between using - must -and -have to - is found in the obligation you want to express.
If it is a law or something forbidden by rules affecting you personally, whether these rules are set by a company or listed at a swimming pool, you use - must -.
You must not steal. (one of the commandments from the bible "thou shall not")
You must not smoke at any of the premises (it is forbidden to smoke at company premises)
You must not dive. (Diving is forbidden)
If it is a rule or very strong advice of a more generic nature, or you are not sure it will be followed through - have to - is more appropriate.
You have to be back home by 23:00. (You are told to be back but will you?)
He has to see a doctor in order to check out the pain in his leg. (He should see a doctor, but will he?)
We have to watch out to not gain more weight. (We have to eat less, but will we?)
We had to wear a school uniform. (An obligation of a more generic nature)
Try it yourself
Please find below the link to the exercise and the document itself for downloading directly:
Even with the use of 'must' and 'have to' it is all about the intonation. Your tone of voice and where to place the accent will tell you how strong the order is. If you want to hear it, book a lesson!