The hiring manager probably has several candidates, internal and possibly external as well, to choose from. She wants to make the right choice for the team and the business. Here are some of the primary factors she will most likely consider:
Can you do the job?
The manager wants to make sure you have the skills needed to succeed. These may be technical skills or "softer" skills such as customer service, supervisory, or communication skills. The manager has identified a list of skills and performance characteristics that she considers important to the success of the role.
What you can do: Identify your own skills, strengths, and experience. Actively manage your personal brand at work to become known for your best attributes, particularly those valued at the next level. If there are skill gaps between the role requirements and your own experience, invest in training, volunteer for projects to gain experience, or find a mentor to help you obtain the necessary skills. Make sure you handle your current responsibilities calmly and capably; if you're consistently overwhelmed at your current level, it will be hard to make the case that you're ready to take on a larger role.
Do you want the job?
The fact that you want the job may seem obvious to you, but managers are not mind-readers, and she wants someone she knows is interested in the role and the responsibilities involved. Many people make the mistake of assuming that "someone" knows they want the job, and waiting to be offered the position.
What you can do: Before proceeding, first make sure that you really want the job - that you will enjoy the role and responsibilities, and the change will help you reach your personal and professional goals. Then ask for what you want. Clearly state your interest in the position, and ask to be considered for the role. Be prepared to share why you want the job and why you're the right person for it.
Will you make me look good?
The manager wants to find someone who will help her achieve her objectives, and whose presence will make her look good to her bosses.
What you can do: Pay attention to the characteristics, actions, and thinking that people already at that level demonstrate, then behave and dress like you're already there. This shows the manager that you're up to the task and will conduct yourself accordingly. Identify what goals are important to your manager, and align your actions to help achieve her metrics and objectives. Focus on completion of tasks and achieving "wins."
Will you make my job easier?
The hiring manager prefers to find someone who will be able to step into the position easily, handle the responsibilities, and solve problems. If she thinks a candidate will require a lot of training, hand-holding, or create problems or headaches for her, she will look elsewhere to fill the position.
What you can do: Cultivate a solutions-focused mentality. If you need to highlight a problem to your manager, also provide a possible solution. Keep problems off her desk, rather than piling more on. Complete tasks well and on time. Be credible and consistent - others need to trust that if you say you will do something, you will do it. Cultivate positive relationships with colleagues and demonstrate the ability to work well with others.
By focusing on how you solve the needs of the manager and the organization, and clearly showing how your value aligns with the responsibilities of the position, you will look like the ideal person for the role. Having a solid record of accomplishments and achievements using the core skills the manager is looking for indicates your ability to handle future roles as well. Just don't forget to speak up and ask for the promotion too.