Use Lightweight
Start with fabric, press it, and back it with an adhesive, like Steam a Seam 2 (I prefer the Light version) or Heat n Bond Lite.

Benefits
Lite Steam A Seam 2 (LSAS2) has a pressure sensitive side so that, when paper is pulled away after fusing to fabric, you can finger-press it in place. You can reposition it as desired and it is more convenient than using temporary spray adhesive on multiple shapes.

Fusibles keep edges from fraying before embroidery and help hold the piece to the base fabric without puckering or bubbling. The light versions of fusible will also keep your embroidery soft.

Print out the placement lines of your applique design. You can isolate the shape using an editing program like Embrilliance. Print placement lines (at actual size) on paper and use it as a pattern with which to cut out your applique fabric. 

Steam-A-Seam has a one-inch grid on the paper side which makes it very easy to pre-cut pieces slightly bigger than the size of your applique shape. 

Fabric should be cut along the lengthwise grain to prevent stretching. After fused fabrics are pre-cut, how do you know which way to position the pieces when you cut? Mark them. Mark the paper side of the fusible with an arrow showing which side is upright. That will keep the lengthwise grain where it belongs.

Some shapes will mirror each other, which means that shapes must be cut in reverse. Keep that in mind when cutting applique shapes. 

Trim away stragglers and save decent-sized scraps. You never know when they could useful. Add direction lines to them and place them in a zippered food storage bag. 

Have any other tips? I'd love to hear them!