Whether you have decided to completely change your career, or are simply moving from one company to another in the same field, there are a couple of things you should consider doing before sending your job application in. First, make sure that your resume is up to date and organized well. Be concise, yet emphasize how you have succeeded. Rather than simply listing job responsibilities, provide actual numbers and information that demonstrate how you have dedicated yourself to leadership, team work, and self-improvement. Get your resume looked over by a career counselor if you want to make sure it is fully presentable and impressive.
Secondly, make sure that you have references lined up and ready to speak highly of you. Choose your references wisely. It is best to stick with people who know you well, and can speak positively about your skills, abilities, and character. Do not list someone on your reference list before asking them first. You want to make sure that they are willing to be a reference for you, and that they know enough about you to provide a good reference. It is always a good idea to provide your references with information that may clarify your background, so that they are completely prepared for any phone calls that they may receive from prospective employers calling about you. A resume or curriculum vitae, personal statement, past publications, etc. are just some of the many things that you can provide so that your references get a full picture of who you are as a person.
Lastly, take adequate time to prepare yourself for the interview process. Read up on possible questions that you may be asked, and practice, practice, practice. Do research about any companies you are applying to so that you are ready to answer any questions and prove that you know your stuff!