Some thoughts on getting an agent (the first step in being traditionally published) 

• Finish your book.
• Go through it with a highly critical eye. One way is to read it aloud to someone or yourself or your cat. Another is to have your computer read it to you.  
• Once that book is as good as it can be, go back through the first five or ten pages again. Word choice, poor grammar, spelling errors - the agent and then the editor is looking for a reason to say no early on. Don’t give it to them. The first few pages should be as perfect as a poem. Make sure you are beginning your book in the best place.
• Figure out some books out there like your book. Do not pick someone like Stephen King or George RR Martin - use more grounded, but still well-reviewed and decent-selling comparisons.  
• Start submitting it to agents. Use AgentQuery.com, QueryTracker.com, or Publishers Marketplace (see if you can join for a month to make it cheaper) to search for agents who like your kind of thing.  Look in the acknowledgements of your comp titles.  
• For examples of query letters that work, google something like "query letters that worked” 
• Follow the instructions for what they want, which might be, say, a query letter with the first five pages pasted in.  
• You will probably realize later you wish you had changed some things about your query letter, so don’t send it to all your top picks the first time.  
• Repeat as necessary.  
• If funds allow, go to a local writing conference - new agents will often be there, looking for new clients.
• Jane Friedman usually has good things to say: https://www.janefriedman.com/find-literary-agent/