To ensure a new background blends well with the subject, match the lighting, color, and perspective of the background to that of the subject. Use adjustment layers such as Curves, Levels, and Hue/Saturation to fine-tune the background’s colors and brightness. Apply a Gaussian Blur if the new background is too sharp compared to the subject. Additionally, use layer masks and the Brush Tool to blend the edges of the subject with the new background, creating a smooth transition that makes the composition look natural.