Water clarity is definitely something to look at, as is the size of the available forage and the existing weather conditions. But to keep things simple, you can choose a lure to coincide with the depth of water being fished. Just remember, there may be instances when a lighter, smaller lure might work better in deeper water than a heavy one and vice versa. Another size component involves the blades. Most spinnerbaits are pre-packaged with the proper size blades necessary to maintain optimum lure balance.
Some baits have two blades, the tandem model, while others have one.
While some companies such as Strike King have modified them to some extent, spinner blades come in three basic styles. They are the willowleaf, Colorado and Indiana. Blade size is dictated by number, with smaller blades receiving the lesser rating. Tandem baits can come equipped with any combination of blades, two of the more popular ones being a small Colorado ahead of a larger Colorado or a small Colorado in front of a larger willowleaf. The size of the blades tend to coincide with the weight of the head.