"Should" vs. "Have to" and "Must"

Should is often used incorrectly to describe a situation where some action is required. For example:
  • Tomorrow I should go to the ward office and pay my taxes.
This sentence, while grammatically it has no problem, does not give the urgency and sense of requirement that the speaker probably intends. That is because the word "should" is used in situations to mean "it would be good", or "the best thing would be". For example, we should all exercise regularly for our health. It would be good for us to all exercise, but if we don't, there is no dramatic consequence. It is not required.

Other examples of "should" used appropriately in a sentence include:
  • You should brush your teeth before you go to bed.
  • I should go to work early today because I will probably have a lot of emails to sort through..
  • Tom knew that he shouldn't eat any more cake, but he did anyway.
Again...in all of the above sentences, should means that it would be good to do or to not do something.

If you mean that doing or not doing something is a requirement, usually with a much more severe consequence for failure, then "must" or "have to" is the correct grammar. For example, the first sentence above should read:
  • Tomorrow I have to go to the ward office and pay my taxes.
  • Tomorrow I must go to the ward office and pay my taxes.
Because if the speaker does not go and pay their taxes, there will be a large penalty, or possibly jail time! It is required that they go to pay their taxes. Other examples include:
  • We must go through airport security before we can board the airplane.
  • You must arrive at the office by 6:45am to unlock the front door.
  • Before we send the proposal to the client, we have to send it to the compliance office for them to approve.
"Must" and "Have to" sentences indicate a required action.

Be careful of confusing the "it would be good" meaning of "should" with the "it is required" meaning of "have to" or "must". When used correctly, they are two similar but very different ideas that can enhance your ability to communicate effectively.