NIB summed it up well. There are some general things that you know in advance will affect the action of the plug: type of lip, how it is bent, weight and placement of weight, shape/size of plug, and where the line attaches. When starting out, try making a copy of a plug in your bag that you like. Learn what makes it work the way it does. Once you have it down, experiment some to learn how you can change the action of the plug. Make several that are the same size and of the same wood. Weigh one in the chin and one dead center. Notice the difference in the action? Try a danny type lip on one, a pikie on another, but weigh then the same. See what difference the lip makes? Conducting such experiments will teach you a lot about how to get the action you want from a plug.
When working on something new, I have an idea in advance what action I am after. By knowing some of the basics, I can design the plug along the lines of what I want. Then comes the testing. Try various amounts of weight, or no weight, placement of weight, type of lip, etc. I often go down to my test pond with a few different lips, lead slugs, drill, wire, and various hook sizes to try out on several plugs. Takes some work, but when the stripers start busting your plug while your partner can't buy a strike, it will pay off
Jigman