I like Sta-Flo liquid laundry starch because it's easy to mix to the strength you want. The strongest I use it is in a 1:1 ratio with water (equal parts of both).
I use this strength for backing fabric, for fabric I plan to cut into bias strips, and for foundation fabric for machine applique. (The foundation fabric comes out stiff enough that I do not have to use a stabilizer underneath for the machine applique.)
My method is to "paint" the starch solution on the fabric. My kitchen island is the right size and height, and I use a regular wall painting brush for the "painting". I paint until the fabric is saturated with the solution, then toss in the dryer and later iron with steam.
Sta-Flo can also be mixed with water to use in a hand spray bottle. I haven't used it this way yet.
I don't typically use aerosol spray starch for a couple of reasons: (1) I always get overspray, which I don't like, and (2) I never seem to wait long enough for the starch to soak into the fabric. This is especially a problem because I do not prewash fabric; spray starch tends to just sit on the surface and not get absorbed into the fibers. Ironing it this way results in flaking or scorching. (3) I always seem to use too hot of an iron on the unsoaked-in spray starch, so I end up scorching the starch and gunking up the bottom of my iron.