As an employee, there are often times when you feel that you want a new challenge or are simply not happy in your current position. Rather than looking for a new employer you may wish to explore internal vacancies. If an internal job vacancies has come up that you wish to go for then you need to ensure that you are fully prepared for the interview which you will most likely have to attend. Many companies advertise jobs internal prior to advertising to the public so if you are looking to move up the ladder within the business, then this could be a great opportunity and mean that you are in competition with a lot less people.
Firstly you need to consider if you have all the qualifications and / or experience that they require. If not, then this does not necessarily mean that you will not be able to apply for the job, just that you will need to explain why you think you are capable of doing it and what experience you have that will help you.
You need to make sure that you have shown your capabilities and trustworthiness in your previous role as employers are unlikely to offer a new vacancy to an employee that has not been very reliable.