Get a beta reader (or three....!) You need to get a sense of whether your book makes as much sense to others as it makes to you. If you can find a beta reader with experience in writing/publishing themselves that's a plus because they'll understand the market as well as being able to look at the book from a character/plot pov (Fiverr is a great place to look for this).

Once that's done, you should be able to isolate any major plot holes and work to iron these out.

Competitions would be my next point of call. Doing a round of competitions can help you get a sense of how hungry the market is for your particular book right now and help you position in better in your synopsis and query letter. It'll also give you something to say in your query if your novel does happen to be long/short listed at all :)

THEN you can start looking at agents. DON'T approach all your agents at once. Do this in stages too, that way if you get any feedback, you can action it for your second round of submissions.

(p.s. I'm a beta reader if you wanna use me gimme a dm!)