If i want my fabric light to Medium starched, i just put the liquid starch in my washing machine instead of fabric softener... I put as much as the container will hold... And wash the fabric as usual. If I want heavier starching, I'll add the same amount again after the last spin cycle, and just run the washing program from the point where the fabric softener is added ( last rinse), then spin and hang dry.
If I want a really heavy starch, I'll place a large bowl or a bucket with a starch/water mix inside my bathtub, put each length of fabric ( still wet from the wash as I per wash everything, or dry) in the bucket, make sure it is thoroughly drenched, hand wing this and then hang dry inside my bathtub as it will drip quite a bit. In summer this can easily be done outside, the worst thing to happen is that your lawn or pavement might have a few whitish spots until the next good rain.
I iron when almost dry, or spray a little bit of water on the fabric to just moisten before ironing if it dried completely.
I never measure the amount of starch, just like I cook and bake... I don't mind if my fabrics not all have exactly the same stiffness... With spraying it tends to be uneven too, and as I have carpet everywhere where I have enough space to lay out fabric or set up the ironing board, I don't like to work with spray starch too much.