You need to be able to show employers that you have creative skills, technical knowledge and the ability to work to a design brief. This will involve presenting a portfolio of your design work, and usually also having a relevant qualification at degree, foundation degree or BTEC HND level.
You could choose a qualification in product design, or a more general design qualification that offers product design as an option. You could also choose to focus more on technical and engineering aspects of design, or on specific areas, such as furniture, automotive or consumer goods.
You should check with colleges and universities to make sure the course you have chosen covers your areas of interest.
The design field is very competitive, and opportunities are often found by word of mouth, so it will be important to develop your contacts, for example by unpaid work experience or by joining professional organisations like the Chartered Society of Designers.
It is worthwhile researching companies whose products match your style, and making speculative applications.
Entering design competitions and exhibitions can also be a good way of getting noticed by employers.