Since, at the moment, I don't spearfish underwater, I can't comment on that, however icarus pacific seems to have that covered.
However, spearing carp/suckers from shore, I can comment on. First thing you have to do is keep an eye out for the spring run. I've no idea when that will be in Penn, but here in SD, it usually runs the end of april, and again the end of june. The key thing, is to go slow. The carp are busy with other things, so take your time and stalk up to 'em. When I'm bowfishing, I like to stand on a high point, dam, roadbed, ridgeline, away from shore and basically spot and stalk the fish as I see 'em. Keeping at a higher elevation allows you to see into the water better, as well as keeping your silhouette away from the water.
Another piece of gear that will make your time much more enjoyable is a good pair of polarized sunglasses. It'll save you a lot of eye strain staring into the water, protect your eyes from the sun, and also reduce glare letting you see into the water easier.
A word of caution, especially with a handspear. The action is going to be very close, and very fast. Often the water will be murky so you won't see your legs/feet underwater. This can lead to a person getting excited and trying to take a quick jab at a fish that you bumped underwater. Stabbing yourself in the foot isn't pleasant, and there is a very good chance the water is rancid leading to a very painful infection (been there, done that, never again). So remember, always more fish in the creek.