This should be a given, but can't be stressed enough. There are many types of bosses in Salmon Run, and any that come up should be dealt with quickly. If one boss hangs around, another will appear, and so on.

Once there are three or more bosses, depending on their type, it may be too late. You soon get used to which bosses you should eliminate first, but ideally, they should be removed as soon as they appear.