When sewing heavily decorative fabric seams, you'll find that with a regular presser foot, it will be difficult to navigate around raised/uneven edges of the decorative elements. When sewing this delicate seams, us a zipper foot instead if a regular presser foot. However, in order for the presser foot to stitch smoothly along the seamline, it is important to first, remove the decorative elements from the seam allowance area. A smooth, flat seam allowance will allow the plate of the zipper foot to feed the seam securely through the stitching process.
The beauty of a zipper presser foot is that the needle can align to either the right or the left side of the the presser foot, which is about half thinner than a regular foot to start with. When sewing decorative fabric seams, the needle should be aligned to the left of the plate such that the needle can stitch next to the raised/bulky decorative elements. The seam allowance layers (which should not have any decorative elements) will be fed under the presser foot plate as the stitch is applied.
Using hand basting in lieu of pins, will keep the seam edges stable and perfectly aligned in the stitching process.