How do you get drywall patches to blend?

Whenever I patch drywall with tape and mud. It leaves a smooth spot. The more I sand, the smoother it gets. But if I don't sand down, there is a blob. How do you get the patch to match the texture of the drywall?

Where I live in Texas the walls are all textured. I have matched the texturing when drywalling by lightly going over the wet mud with a dry paint roller. You could also try a sponge. Practice first so you can match the texturing. I added a closet to an existing room and no one could tell where I had started and stopped the texturing.
Sand it smooth first - then add a bit more mud to texture.

spray it with texture paint, comes in a spray can at hardwares,

do you use spackle to smooth and then sand it?

I have the same problem sometimes. The texture you speak of is probably from painting. Use a really thick primer and a roller to get that drywall textured look to match. Then when the primer dries, roll the matched paint color on. One good technique is to let the paint dry a little bit, then go over it again so it gives a better textured look. Good luck

one way is to make sure the mud is very wide, 12 - 16 inches. Sand down making sure to use the wide strip of mud to hide the difference between drywall joints. Then you need to use a high quality latex primer before you paint.

Second way (and this takes some serious skills) is to layer a very thin layer of paster across the entire wall, This layer is about 1/16 on an inch think. Usually need a pro for this.