It starts with what you make your collar out of. I have found plain weave linen, a little heavier than you might ordinarily make a shirt out of, to take the starch best. This is a good economical solution, 5.3 oz from Fabric-Store.com.
An example of one of my own attempts to deviate from this- I made several collars out of cotton twill, thinking I had really stumbled onto something, but when I tried to starch them, they just turned into a limp, powdery mess.
The examples I'm going to use here are collars I made for the early Victorian period (and as far back as the 1820s) that button in the center front, tie in the back, and stand straight up (actually, they kind of gradually mold to your contours as you wear them).
First- they must be CLEAN. At this point they will be a wrinkly, limp mess, not resembling the end result at all.
Giving credit where credit is due, this fellow's video gave me the foundation of my method:
My Starching Method-
For up to three collars and maybe more- take a smaller sized mason jar and thoroughly mix 1/4 cup of starch (can be just plain off brand corn starch) and 1/4 cup of cold tap water. Then add 1/2 cup of boiling water and mix thoroughly.
Then add the collars and screw the cap on tight.
Get them all thoroughly saturated. For the next hour or more, turn the jar upside down and then back again a bit later repeatedly to keep the starch mixture flowing (and soaking in) evenly through the collars. Then, remove them from the jar, ring them out, and use your fingers to slough off excess water and starch. Hang them up and let them dry until damp. Do NOT let them completely dry.
Now it's time to press them. For a modern iron, be sure there is no water in the reservoir and heat it to the "linen" setting. Also, cover the portion of your ironing board that you will be using in a piece of scrap natural linen or cotton (don't use synthetic- it will melt).
Slowly, firmly, and evenly, run the iron over the collar, working it into a smooth firm surface as the starch dries under the heat of the iron.
They will be stiff as a board, which is exactly what you want! A very tall collar like this may be a bit uncomfortable at first but will gradually shape itself to you and will be fine to wear all day.
If you are making a collar for a later impression that requires heavy starch but folds over:
Follow the pressing procedure in two parts (with your protective cloth) over a tailor's ham, working it into a curved shape as you go.
Do the neck band first, then place a piece of natural cloth over the neck band, fold the upper portion of the collar down into position, and repeat the pressing process on it (with the piece of cloth between the neck band and upper portion; again- working it into a curved shape over the tailor's ham).
Remove the piece of cloth between the neck band and fold over.
Photo by Naomi Faith Hammond Wilson
I hope this helps! There's nothing like starting the day by affixing a clean, crisp starched collar to your shirt.
Yours & c.,
The Victorian Man