Going the traditional publishing route is a life of waiting. You send in a query, and you wait. You get a hit from an agent and they ask for the first three chapters, so you send them and wait. Then they ask for the full manuscript, so you send it and wait. And wait. And wait. Then (lucky you) the real work starts from the publishing perspective.
The biggest mistake I see comes after someone writing a novel and sending it out to agents or pro-pay publishers. They keep clicking on send/receive every few minutes. They check the mailbox two or three times. They twiddle their thumbs and pull out their hair.
What they should be doing, in my lowly opinion, is to send the novel out and start writing the next one. Then send that out and start the next one. The more popcorn kernels in the oil, the more likely one will pop.
The marketing side of things is another specialized skill set you will need to develop. If you already have a decent following on social media and an established website, the agents and publishers will (sometimes heavily) count that in your favor. Consider developing a mailing list and a newsletter. Did you cut out a chapter? Tweak it and send it to your mailing list as a free teaser, or make it a separate but related short story.
There's lots of things you can do to help get your book in front of more eyeballs. The pain in the butt is learning about them and then implementing them.
Authors think that going traditional means that the big-time publisher will do all of the marketing. If you're lucky you'll get a nice writeup in their catalog. Maybe you'll get a starred review in Kirkus. The rest is on you as the author, which is why having a decent author platform/social media presence goes a long way with publishers and agents.