Upgrade to captain asap. Become a line check airman if possible. An advanced degree would be helpful (MBA, JD, etc). Get super involved in volunteer work in your community, preferably one that posts lots of pictures of you doing great things for popular causes. Join every professional pilot organization that will take your money, no matter how ridiculous your affiliation with it might seem. Apply early and often to every major you’d ever consider working for. Don’t get a speeding ticket, and keep your credit score up.
For gods sake, scrub every social media post you’ve ever put up that you wouldn’t feel comfortable showing your great grandmother, on a huge screen, in church on Easter Sunday with a huge congregation of ultra judgmental prudes.
Above all, don’t believe the hype about the “looming pilot shortage.” It’ll never happen. I’ve heard that old chestnut for 25 years now. Robots will be flying the planes before we ever return to the days when majors were hiring private pilots with single engine only time.
(Only partly TIC. There’s a reason seasoned pilots tell the youngsters not to put everything in the “airline pilot” career basket)