Being accurate is essential. This means cutting, measuring, stitching and pressing. Use good tools. I always use a steel tape measure-never cloth or plastic as they stretch. One of the most important things I have ever learned is to measures everything flat on the cutting table-never hold it up in the air. Square block segments up as you work. If they are wrong in a partially constructed block they will be more wrong the farther you go. I just finished making a quilt top using these principles. When I finished I was off 1/4 inch in one direction and 1/2 inch off in the other direction. The quilt is 99 inches square. I recommend watching lots of tip tutorials and adopting some that work for you. There are good ones and there are some not so good ones.