I just finished training at a regional last week. And just completed IOE. Great advice listed so far. I was a 1500 hour instructor (both 61/141) and had about 30 hours of turbine experience (not logable) from a mentor prior to training. Attitude is everything. Everyone has different experiences (flying and non flying) that can help and hurt them. Be a sponge and follow the airlines training footprint.
Focus on what you’re learning each week in training, it’s okay to look ahead but in any AQP program it’s stage by stage. If you’re in systems, learn them and learn them well. If you’re in procedures, focus hard on procedures, etc. Having a great attitude is a big part of it. I found that sticking to a schedule religiously helped. But don’t forget to spend some time to relax as well.
The areas where I saw people having issues was attitude, thinking that the program should be run differently or that “at my old carrier this is how it was done” beliefs. Thinking the airline will spoon feed you is not an accurate assumption. Going to a turbine or Part 135 carrier may help, but I would go to the fastest route towards 121. Sure knowing a bunch of instrument stuff can help, but it’s not going to put you that much ahead. My sim partner was a Blackhawk pilot with 0 glass time, and the absolute bare fixed wings mins required. He passed training with no failures and set backs what so ever. Was it easy for him? No. But it’s more than doable. If you have good airmanship skills, can interact well with people, and know how to study you will be fine. Most airlines give you access to literally every training resource you will need on day one. Learning how to use the resources appropriately will help you tremendously.