Cornstarch mixes the best with cold water. It may take some experimentation to create the consistency you desire. Don’t worry if the mixture is a little too thick. You can thin it out later with water.
After cooking the cornstarch mixture, add it to a heated up liquid. You have more control because you can as little or as much mixture to the liquid as you’d like.
If you are only cooking the cornstarch mixture, you should pour it in a pan and turn it to medium heat.
You may need to heat up and stir the mixture again after you add water.
Add seasoning, like salt, in small increments to avoid over-salting or over-seasoning the recipe.