An problem for me had been stabilizing my designs.  It never seemed to me that I used the correct stabilizer for the project.

I got a simple, general guide that will work most of the time, from a professional and it is so easy that anyone can use it. 

Think in terms of heavy denim.  It is usually stiff, not moving much and very stable on its own.  In most  cases, you would not need to stabilize this type of fabric.  After washing, it changes, but we are dealing with the embroidery on the original document and washing embroidery will generally relax your design, but if originally properly stabilized, it wont matter, it will take the characteristics of the fabric.

So, the fabric you are using needs to be as stabile as the denim.  Therefore, the lighter the fabric, the more stable it needs to be. 

Water soluable tends to be the least stable, then comes tear away stabilizer and finally comes cut away stabilizer.  On a t-shirt, I would use a heavy weight cut away, adhere it to the back of the knit of the shirt AND  place a water soluable on top of the fabric.  If you can mentally think of each of these together, they would be very close to the denim we discussed earlier.

Best wishes to you and yours, Pat