I mainly print mine out on cheap copy paper, that way i can tailor the size of the target to the range im shooting at, or the type of weapon i'm shooting.
for open sights i like a red O with a white center just big enough to see the outline of my front sight in the target surrounded by a visible red ring. That helps me center consistantly.
for my scoped rifles i'll do a 1 or 2 inch square turned 45 degrees, (think square diamond) and the corners of that rotated square help me hold the crosshairs consistantly when shooting for group size.
The eyes arnt what they were many moons ago ya know?
Now when i went through the LEA many years ago, much of the time we shot at the back side (blank) of targets, as that was a good way to concentrate on center of body mass, without being distracted by target rings. i still do that some now, particularly when prepping for hunting season.
Oh and if you can find some of the heavy paper seperators, used in some shipping containers, they work great to mount targets on, & ball or bullet cuts a neater hole at least til you shoot the center out of it LOL.