I keep control over my stitching by holding my work between my thumb and forefinger close to my stitching.
The tip of the needle slides down and slightly under the seam allowance.
The stitch is taken behind the thread that has just come through. This is to make sure the stitch you take next is perpendicular to the stitch already taken. The needle goes through at an angle and if you take the stitch in front or opposite the thread, the stitches will end up being angled and you don't want that.
As the stitch is taken, I use my left hand to fold down the work and bring my needle up. This will ensure that you are catching the background fabric and makes the stitch easier to take. Pick up a couple of threads in the seam allowance, not on the top of the applique piece. Practice and it will become natural after awhile.
Not every stitch I take is hidden but doing it this way has improved the look of my applique over time.,
Tip #2 Controlling the tension.
Remember my puckered work around the stems? I had been pulling the thread too tight so I've fixed that problem now by paying attention when sewing on bias stems. I like to glue baste the stems in place and it's important not to stretch it when you are positioning them.
As I pull through the thread for each stitch, my last two fingers are placed so that the thread wraps over them. This controls how tight I can pull the thread. With a bit of practice, you can get into a rhythym. You don't want the stitch to distort the applique but on the other hand you don't want the stitch too loose and popping up.
I like to use cotton thread but some like the YLI silk thread for applique. The silk is hard to keep in the eye of the needle because it's so fine and slippery.
Here's one way to secure the thread. Thread the needle and place the tail end between the thumb and finger. Grip it tightly. Push the sharp end of the needle through the thread to pierce it. Pull the needle all the way through and you should have it secured at the eye.
The second way is to wrap the tail end over your thumb or finger and pierce the thread with the tip of the needle. Pull the needle through.
In both cases, this is what it will look like before you pull the needle through.
I always cut my background larger than required because there will be some distortion. Don't judge your applique until it's pressed. I press on the wrong side with a folded towel underneath before trimming the block.
I hope these tips are useful to some of you. I don't consider myself as all knowing when it comes to applique. I consider it an ongoing learning experience and am always looking to improve.