If you get a definite bite, yes, set the hook instantly. I set it again after a few seconds to drive the thick hook deeper. That tough cartilage resists a hook, so be sure the barb is sunk in.
But all too often the bite doesn't feel at all like a bite. A mushy feeling is all I need to react. Or many just he line moving oddly. Any change from what you expect, what you've been feeling, ought to be met with a hookset, with some caution in certain cases. Over time you learn the exact feeling of a jig bumping a branch or rock, or crawling over or through a weed. Besides a Zara Spook as my one and only hard topwater lure for several years as a teenager, home-made jigs were our staple bait. I had a bucket of those at any time, knowing I'd leave many a day in the lake.
It took what seemed forever to learn to catch bass instead of "limb, stump or rock" bass. A partner could watch and make the call, declaring "stump bass", based on how the line and rod tip moved. If the line tightens quickly the object is solid, like a rock. If the object is limber the rod tip bows at a rate equaling the reeling, signaling tree branch. Sometimes, if the water is calm and there is no noise a partner can hear a jig hit a rock, but not a stump. If hung on a rock pass the boat back over it and jiggle the rod tip up & down to release it. If on a stump I figure on using a paddle or knocker to release it, but start with the rock release first. Take care not to drive the hook deeper.
With information like that I began watching the rod tip and line instead of the water so much. It does no good at all to be watching birds, clouds, waves, and stuff. If you watch the water keep an eye on where the line enters it. Keep another eye out for swirls in shallow water close to where the jig should be. That could be a bass making a dive for it. You need several senses going. Feel, sight, and experience. A solid bite snaps the rod tip slightly as the line gets tighter. Sometimes the rod tip dances the slightest. Sometimes the line just takes off towards you. Maybe you are reeling and the line seems to stay put, the little line entry dimple in the water staying put instead of coming closer. Bass is likely bringing the bait up. That's a bad time to set the hook, whether coming up or towards the boat.
Another very common feeling is a jig entering a weed bed. If the leaves are coarse the line sometimes "sings" through the rod (no sound), and the rod tip bows and releases at a high frequency. With a high modulus graphite rod of high quality you learn to identify the line sawing over rough leaves and stems. The jig drags heavier and produces the mushy feeling, loading up a little, unloading , loading. But a big bass often makes that mushy feel. If the jig stops after doing that, set the hook. Lots of times a bass will inhale the jig and stay put crunching, so the line doesn't want to move. But sometimes the bass will yank and swim, a no-brainer time to set the hook, unless coming to you. Let the bass turn first. There's different opinions about that. Many good anglers prefer not to lose the slim chance of setting the hook anyway. Waiting for the fish to turn risks that big bass deciding something is wrong, spitting it out. Another popular technique is to set the hook anytime you feel anything at all. Some believe their catch rate is higher, but they also often have a jig sponsor, make their own in large numbers, or have a lot of jig money :baitmonkey:
Jigs are well known to appeal to larger bass than little ones. Any big bass around smaller ones will likely be the one right over the jig, eyeballing it, claiming first dip in the bowl. There's a definite "pecking order" among bass, the larger getting the first bite. The feel of the large bass is quite different from that of small bass. They are less likely to take off violently, while small bass are likely to make a run with it to get away from competing bass. They don't have the vacuum power like a big bass, so attack more directly, while the big bass can suck the jig up from farther away, using fewer calories. The big one can easily swallow the jig on first strike, crushing it, while a small bass might only get the jig in the lips until it can take another solid bite deeper in its mouth, so seeks a safe place to finish the job. While taking the jig elsewhere is the time to set the hook before it spits it. The risk of tearing out of the lips is higher, but that might be your only chance. Pay attention to where the hook pierces to refine your approach. If you get any action from a bass your partner needs to drop another jig in the same spot, as the other bass are alerted to the possibility of another chance of eating, and are more excited than they had been. Two anglers can often catch a large number of bass from one spot before the fish move away. As each bites urine is released with pheromones that alert the others to a hazard. Catch all you can as fast as possible and don't release them to the same spot immediately. Put them all in a livewell until your limit is reached, then release 100 feet away if done with the spot. If the spot is a real favorite among those bass they will frequently return to it for another round of catching an hour or two later.
Jim