Preventing tram lines when clipping is an essential part of ensuring quality results. It is important to use sharp clippers and blades, as dull blades often cause lines. It is also essential to go over the same area multiple times in different directions to avoid lines. Before clipping, use a comb to separate the hair and ensure it lays in the direction of the cut. Finally, maintain a steady hand and speed on the clipper to ensure the lines are correctly blended.