When purchasing a home, it's crucial to be aware of what not to do. Key mistakes include overestimating affordability, getting emotionally attached, making large purchases, and altering your financial situation, such as switching jobs or co-signing loans. Avoid large cash transactions and applying for new credit, as these can impact your mortgage approval. Stay organized with finances and maintain good credit to ensure a smooth home-buying process. Prioritize pre-approval and avoid distractions to secure your dream home.