Check for an existing number first
A National Insurance number stays with you for life. Check your official documents and accounts before applying again. A change in personal details does not mean you need a new number.
The number is not permission to work
You can start work before receiving the number if you can prove your right to work. An NI application does not replace immigration conditions. The application is for people living in the UK who have the right to work and are working, looking for work or have a job offer.
Practical preparation
Use the government service and review the requirements for your circumstances. Keep details consistent with your documents and store the application reference securely. Avoid sharing your number in public comments or unnecessary messages.
Before submitting
Check your correspondence address and access to your email. If you already have a number, use the find-your-number service instead of submitting a duplicate application.
Sources and next step
Local rules can differ. Consult the source for your part of the UK before acting.