I use 3/8" seams with 2 and 3/4 cut width of binding. The only pinning I do is the first couple of inches, helpful to me when positioning the quilt under the needle. I sew about 6" and then stop to test that the binding folds over exactly right. Different thicknesses of fabric and batting can make a difference. When I get close to a corner, I use a seam gauge to find 3/8" up and stick a pin only in the quilt at that point perpendicular to the seam. I sew slowly to the pin and stop when I get to it and backstitch. I only trim out the corners when there is too much bulk. Normally there is no need.