This list is handy to have. When crocheting in the round, increasing the number of times each round according to the stitches used and the number next to it will usually prevent your work from rippling or bowing up. Of course, you’d want to evenly distribute the increases throughout the round. If you want to make a hat, stop increasing and your work will begin to form a bowl like shape. Continue to crochet without increasing and you end up with a hat or a bowl.
If you are working with sc and you want your work to be stiff, then you crochet tighter stitches or use a smaller hook. If you want your sc to be softer then crochet looser stitches or use a larger hook.