The legal term for excluding someone from your will is called negative intent, but that doesn't necessarily mean it's bad or wrong to exclude someone. You may no longer have a relationship with a relative, or perhaps you've already given a person a share of your estate. The law allows you to specifically exclude an heir from your will by either not mentioning him at all or by writing a specific phrase that outlines your negative intent.
Find out if the law allows you to simply leave a person out of your will, or if you need to specifically exclude someone by including wording attesting to that fact.
If you are required to put your exclusion in writing, state in your will, "I intentionally leave no property to my (son, daughter, other relative)."
Add the names of the people being excluded.
Write a short letter explaining why you are excluding that person from your will. Do not include this letter in the will -- store it with the will instead.
If you have a solicitor, get them to keep a copy in their offices, in case all your papers at home get destroyed or lost.
Check with a solicitor to see what laws apply to your situation.
If you exclude a person (for example, a minor child) from your will who is not allowed to be excluded by law, that person will end up receiving their share of your estate anyway.