Hard plastic or wood baits are designed to attract the fish's attention and get them to try to eat it. They can come in sizes ranging from tiny one-eighth ounce baits to huge baits weighing several ounces. All are designed to look like food and most have two or three sets of treble hooks on them. You give them action by casting or trolling and they will cover the water from the surface to many feet deep.
Plugs that float at rest but dart under the surface when moved are very popular for game fish ranging from bass to bluefish. They have a small lip near the head that makes them go under when they are pulled in the water. Most dive a few inches to a couple of feet, and by pulling them under and letting them float back up they look like hurt baitfish, an easy meal for a predator.
Most floater-diver plugs are long and thin and wobble from side to side when pulled. The action can range from a tight wiggle to a wide wobble and these plugs can be reeled or trolled just under the surface. They can be fished in very shallow water or reeled over underwater weed beds that come near the surface. They're also very effective around any kind of freshwater shoreline cover, or in salt water around offshore structures like oil rigs.
Natural colors, like silver or gold sides with dark backs and lighter bellies, imitate the color of baitfish and are good choices. Sometimes a very bright color like chartreuse or florescent orange will attract attention better in stained water or offer the fish something they don't see every day. You should start with a few natural colors in different sizes but add a couple of bright colors, especially if local fishermen say they're good.
Some colors of artificial baits may be very popular in a particular area and produce well there but not be as effective in other places. When traveling or fishing new waters, check with local tackle stores to see what's popular before buying plugs to use in that area.
Although most deep divers float at rest, they have big lips that make them dive deep when reeled in. They're designed to dive to a particular depth and run there, so you can choose one to fish just over a weed bed six-feet deep, or another to bump the bottom in fourteen feet of water. This is important when the fish are holding at a particular depth, too, because you can run the bait right in front of them where they're holding.
A lipped crankbait.
Deep-diving crankbaits are very popular in bass fishing, and most tackle stores will have hundreds on display in a lot of different sizes, styles, and colors. Some will be painted to look like fish and others will be in bright colors never seen underwater. All will work at different times and in different places. Start by buying a few in natural colors that dive to different depths and add others as you need them.
You can buy one style of plug in several sizes that will cover different depths of water. Shadraps by Rapala come in sizes ranging from #5 to #9, and each size will run a different depth. Purchase a couple of basic colors in each size and you can cover different depths easily.
Deep divers come in a lot of different shapes and their shape controls their action to some extent. Usually fat round plugs have a wider wobble than thin flat plugs but the lip of the plug is more important. Wider lips usually mean wider wobbles. The size of the lip also controls the depth the plug runs. Plugs will small lips run shallower and those with big lips dig deeper.
Lipless crankbaits are flat or teardrop shaped and are designed to wiggle when reeled in. They usually sink at rest and have a tight wiggle. Many have a lot of rattles in them to make a lot of noise as they come through the water. They can be fished at any depth depending on the speed you retrieve them and they can even be jigged off the bottom.
Although crankbaits have multiple treble hooks that look like they would securely hold any fish that hits, they are notorious for having fish come off them. Good sharp hooks are extremely important when fishing any kind of plug, so sharpen them often.
Some plugs of this design are made of lead or other metal that sinks fast. These must be reeled very fast to keep them near the surface but they're very effective when fishing deep water. You can either let them sink to the bottom and hop them along it, or let them sink to the depth the fish are holding and work them back at that depth.