If you're entangling because of the fight with the giant herring, that is perfectly normal. But if get entanglement from normal lowering or retrieving of line, then it's probably because you're doing it too fast. It is recommended that you lower your rig down gradually with some tension on your end. Letting the bait/rig drop in free fall often causes the bait to spin and gets rig entangled on itself.
Anglers often use spreaders for to reduce this problem, especially if they're using a rig with long hook line. There are many types of spreader for different application, you can to go down tackle shop to have a look.
Here's an example of a spreader, this particular one allows line to go through. It's suited for near bottom with a single hook configuration.