Learning to ink and traverse walls will improve your Salmon Run game by 100%. For example, it instantly trivialises Grillers at anything under Professional. Salmonids can't go up walls, and many of them can't even hit you effectively inside a wall, and going up walls is often quicker than alternative routes.
That's my major tip for making Profreshional. I guess the others would be: take out Flyfishes at the earliest opportunity. If there's more than one Flyfish active, use your Stinger. Learn how to cope with Maws as quickly as possible. Many of the boss types lock onto one player as long as they don't move out of range, watch their movements closely and figure out whether they're going to go for you or whether you can move around them (Steel Eels). You can't be wiped out as long as a bomb is active, and bombs are like healing explosions. Worst case scenario, you won't wipe out until after the entire drowning animation has played out, which takes nearly 5 seconds. Regularly use 'This way' to cope people. Pay attention to the tide markings at the start of every level. Learn what your weapon is for - like, if you have a weapon which needs to charge, you are a support role, know your place.