Scoring the loaf before baking is not decoration; it is control. The cuts you make are the only places the crust can open, and the loaf will expand from the weakest points you give it. Without a score, the crust cracks wherever it pleases.
Use a blade or a very sharp knife, and hold it at about 30 degrees to the surface for a slash that opens into an ear. A single long slash down the center of a batard, one third to one half of the depth, is the classic cut; a lame held flat makes a clean lip. For round loaves, a simple cross or a spiral works.
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Score confidently and quickly, with the blade already moving, right before the loaf goes into the oven. Hesitation shows as ragged edges, and a slow drag drags the dough.