JLURE, it is easiest to start by coping existing lures first. As you learn the basics, it becomes easier. Also, some types of baits are just super tough to balance.
A low center of balance is key to most styles of lures. Other lures, like the flatfish and swimwizz, are not critical on low center of balance.
As mentioned, the weight and position of hooks works as a ballast on many types of lures, but some need more.
Additionally, it also helps on some lures to have a top that floats. Am am working on a lure that requires that the top be less dense then water, and the bottom is much more dense. If it does not have that balance, then this lure spins or at least rolls onto it's side.
If you could post a picture or two of what you are trying to to make, on the Makelure.com web site, then we might be able to make some suggestions.
As for the platic like what Larry is using on the Diving Frog, well that is not so easy. The Flex 80 should be close to it, but River2Seausa is making the actual lures. The link to the Flex 80 is
http://www.alumilite.com/Category.cfm?Category=Casting Resins . The material is not clear like the plastic, but perhaps.........