To understand the impact embroidery is going to have on the products upon which you are placing it, you first need to understand how the various different fabrics affect the designs you are embroidering on them.
Woven Versus Knit
Knits stretch and because of that they require a stable backing and enough underlay to connect the fabric to that backing so that the knit can't move during the embroidery process and in doing so, cause the design to become distorted. Woven fabrics are a lot more forgiving, they only stretch on the bias, so if they are firmly hooped and have a minimum of underlay and a sufficent backing, you should not have to worry about design distortion.
Needles
The size of your needle should relate to the weight of your fabric, a heavy weight fabric such as canvas or denim requires a larger needle. for fine fabrics you want to use a small needle for example, a 65/9 or a 70/10 as a smaller needle will make a smaller hole and do less damage to the fabric.
The point of the needle is chosen by the fabric, ballpoint for knits and sharp for woven fabrics. Ballpoint needles will push the fibers of the knit aside so that they aren't broken in the embroidery process which would cause the knit to run. Sharp needles are best for woven fabrics because they cause the least amount of friction as they pierce the fabric and make the cleanest perferation, helping to keep your lines crisp.
If you are embroidering on a fabric with a texture, whether it is knit or woven underlay is essential for flattening out the fabric so that the embroidery is not lost in the indentations or overemphasized in the raised areas. Fabric with a definite pattern such as twill or pique require a running stich underlay along the edge of the columns to keep them from following the grain of the fabric.
Each fabric has different needs once you understand how to inherent differences of
the array of goods you embroidery you will understand how to overcome them.