However, whats larger for a bluegill may be smallish for a crappies, and whats large for a crappie may be unappealing to a bluegill. If I am targeting crappies, I will often start with a jig in the 5 to 6mm range, with hook sizes of #12 or #10. I team this with an IceMite Magnum from J&S Custom Jigs.
If I am targeting bluegills, my start bait is usually a little smaller. I tend to use jigs in the 4mm size range, with hooks in the size #14 or size #12 range. To stay with the large theme, though, I often team these with a GoJo from J&S. This plastic is about an inch long, but has a main body with twin legs off the side (kind of looks like a cricket) and offers a large profile.
Color can also be an important factor. If the water is clear, I often start with darker colors, ie reds, browns, purples, and blacks. In stained or dirty water, I use brighter colors, ie white, glow, hot pink, or chartreuse. My first color choices are often those that I have a lot of confidence in.
If the fish are looking at the larger presentations but not eating it, there is a sequence that I use. First, I change the colors of my plastics, staying with the same size range. Sometimes, its just a matter of fine tuning the color to get them to bite.
If I'm getting short bites, or if fish are actively approaching the bait but not taking, it may be time to move smaller, but stay with the same colors. If I was using an IceMite Magnum, I will go to a regular IceMite. If the GoJo isnt working, I will go to the slimmer profiled IceMite. If I was using the IceMite, I would go down to an IceMite Jr. Adapt, adapt, adapt.
Same for jig size. If I'm not catching fish on the larger jig, go smaller. The smaller, lighter jigs are easier for the fish to take reliably, but fish slower. Sometimes it takes jigs in the 2.5 to 3mm class with tiny size #18 and #16 hooks just to garner a bite.
Sometimes, its other factors that prompt a change. For instance, I may land on aggressive crappies that will readily take a magnum sized presentation. But as the day progresses, they may drift deeper. Now, a larger presentation has more water resistance, therefore falls slower. Sometimes this means I cannot get to a fish before he moves away. In this situation, I may use a smaller plastic tail simply to get down even faster.
Finally, bait versus plastic. I will almost always start with plastic, and run through my size and color options before I switch to live bait. I don't like having to check my jig after every missed fish and constantly be re-baiting. But, again, if it takes meat to get fish, then I give them meat!
The moral of this article is always be willing to adapt. What may work early in the morning may not get as many fish later in the day. Don't be afraid to change things up, even just a small tweak, to get things going.
Good luck out there!