All the comments about attitude are are correct. I saw a guy with previous military helicopter and airline experience wash out because of his work ethic and attitude. But, it’s not just about attitude. You can get through Indoc, Systems and Procedures Training by paying attention and studying hard. The sims is where the rubber hits the road. I saw 4 people out of 30 fail in the sims.
Almost everything you do in the sims is an instrument procedure. This is why the CFII is useful. For example, can you translate ATC instructions into intercepting radials? “Intercept and track inbound on the CVG 074 radial”.
Get as much glass cockpit time as you can. Everything in the cockpit is glass and you want to be able to interpret it easily.
Try to get some experience in the National Airspace System. If you have any friends who fly King Airs, or Citations and you can tag along on a trip with them, just observing. Three or four days of seeing how everything works, STARs, DPs, how it all works together.
Check out the articles at
Jeppesen Chart Clinic Jeppesen Chart Clinic Articles (from AOPA Pilot magazine). The airlines use Jepp plates, not NOAA. This is good for the interview too.
Read The Turbine Pilots Manual by Brown and Holt. All good stuff. It makes going into systems easy, because you understand the concepts.
Study for your ATP written with something like Shepard Air. Sure, the airline will probably give you a free copy, but you want to know that stuff going in. If money is an issue, buy the Gleim book and work your way through that.
Hope it helps!