Common DIY flooring mistakes include poor subfloor preparation, like neglecting to level the surface, which causes uneven floors and plank gaps. Tight perimeter cuts can lead to warped or buckled edges, so always allow expansion gaps. Sloppy door jamb cuts without proper undercutting hamper plank movement and look unprofessional. Using low-quality materials can result in chipping and water damage, especially in pet homes. Taking time to prep, plan layouts, and buy mid-tier or better materials avoids these pitfalls effectively.