In the same boat, retiring, haven't flown since '06. Here's what I've learned through the process (I was hired by SkyWest):

Get the ATP done NOW, before the August insanity. There are other threads talking about that.

You are VERY marketable at the regionals. You'll have to get current/qualified there, get about ~300 hours, and you should be marketable at the majors. I've been hearing the same things as you from my buds at the majors - just get current!

If you haven't done Emerald Coast Interview Prep, get it done ASAP! They know what they're doing, prep you well, and are also military guys (now flying for the majors), so they are the right guys to get you prepped.

Start studying now. FAR/AIM, Everything Explained for the Professional Pilot, The Turbine Pilot's Flight Manual, everything there is on Jeppesen charts/plates, Aerodynamics for Naval Aviators, ATP Oral Exam Guide, Mental Math for Pilots.

If you're applying through airlineapps.com, make sure to leave no date-gaps in assignment history, etc. The info you put on there has to be hyper-accurate. There are other threads (i.e. Delta hiring news) talking about some of the quirks of the airlineapps process.

Some of the regionals have simulators as part of their interview process. You need to go pay for sim time to figure out these wacky 1940's era civilian instruments/avionics. Seriously.

Get on airlineinterviews.com and start getting gouge on the companies that you will interview with.

Expect to be hired at one or more regionals pretty quickly - as best I can figure this gig out, take the one that you will know you can sit reserve in your hometown. Commuting to sit reserve for $1,000/month is no bueno.

Good luck, pm me if you want some other gouge!