Do you want to work at Delta?
If so, go to as many job fairs as you possibly can if Delta will be there. Get as many LOR's as you can. Network. Update your application weekly. Further yourself in education. I got my Masters while flying and everyone made fun of me. Maybe thats what got me an invite.
Do your best. Keep a clean reliability report with your current job.
You will get an invite. And if you havent yet, at least you know you're doing your best.
I was fortunate enough to get the invite. It only happened after I talked to a recruiter at WIA. Who knows what triggers what or what is the magic formula. Do everything you can.

I have a few skeletons in my closet and my chances of getting hired are slim, but I assure you that I have prepared the best I know how.