Research extensively the topic of career choices before you write the introduction to your thesis. Consider consulting the U.S. Department of Labor for statistics on the annual income and hourly wage levels of different professions. Also consider reading various economic and sociological texts about how people make career choices. Consult your local librarian for a list of the most relevant resources. Compile a list of resources that you plan to review based on the time you have to research and write the introduction and review as many of those resources on the list as you can before writing.
Write a draft of the introduction that includes a rough idea of what you think the paper is likely to explore. It is often hardest to begin writing the introduction to a major paper or thesis, because you do not know exactly where the paper will end or how you will write it. Consider outlining the introduction ahead of time and include the core ideas of your paper in that introduction, e.g., why the thesis is important, what it contributes to the current debate on the topic of career choices and what you will explore in your thesis.
Outline the thesis in full. An outline of a thesis should include a rough draft of the introduction, a list of sources to be included in a literature review, the content to be reviewed in the background section of the thesis, the body of the thesis that includes your arguments and research and then a conclusion that essentially sums up findings and suggests further areas for research. Have another person qualified to write on career choices review the outline and ideas with you to ensure they cover the topic area effectively and will likely lead to a logical, academically-rigorous paper.
Write the thesis in full. If you make any major changes to the paper while writing it, then go back to the outline and edit it appropriately so that the rest of your paper accounts for these major changes.
Rewrite the part of your introduction that once explained what you would do in your thesis to what you actually did do. The initial introduction is used as a method to help you organize ideas. When the thesis is complete, the actual purpose of an introduction is to explain to prospective readers what you actually did in your thesis and why that research and discovery is important to the broader topic.