Please don’t flame for typing errors or anything. Try not to cringe either because I almost did writing this. So I just felt like taking the time and giving input based on my personal experiences on how to get promoted in the APD. The APD guide right now isn't really a guide in my opinion. This could be completely wrong but it's just what I think. Take this for what you want but this might actually help someone, but it probably won’t.
Just as a general tip I wouldn’t get too worried about if you get disciplined or demoted. If you are a good cop and just make a mistake you will get your rank back and eventually get promoted. Just don’t make them too often. Just ask Darwin and Maddog. Also reputation is a big deal in getting promoted. Keep it as best as possible.
Getting Deputy: Personally this is the hardest of them all for most people. Nobody feels like studying for a test on a video game so they usually try and wing it and fail. Some people pass but usually don’t get very far afterwards. So my biggest tip here is to just read through the handbook. It’ll help a ton in the long run and honestly after you pass the deputy test you won’t have to look at it again. You will just learn as you go. Test is super easy if you read the handbook. Trust me.
Getting Patrol Officer: Almost everyone who gets deputy usually gets P.O. if they aren’t a complete retard. To get promoted to P.O. you need to play with Sr. APD as much as possible. You need to try to get noticed by them or you will be forgotten about and end up being a deputy for weeks and weeks. All around just be a good cop and it’ll come. After a while if it doesn’t I would just ask a corporal to recommend you. Play with that corporal a lot and if they are a half decent cop they will recommend to a Sr. APD member if they think you deserve it.
Getting Corporal: To get this one you have to be a pretty damn good cop, get lucky, or be friends with Sr. APD. By that I mean If you are a 10/10 cop you will get it eventually just because sooner or later someone will notice you have been a P.O. for a long time and realized you haven’t fucked up yet and recommend you. Ask Poro. You could just get lucky and have your best moment you have ever had on the APD and a Sr. APD member just happen to see it and then boom you get recommended. The final one is to be friends with a Sr. APD member. It helps a ton. If you are friends with them you play cop with them and they get to see you play cop more than anyone else because you are their friend and they like playing with you. Giving you a pretty big advantage when to comes to promotions.
Getting Sgt: Although I haven’t been a Sgt. I feel I have a pretty good idea on how to get it. You either have to do something impressive and be a 11/10 cop or be OS/friends with Deputy Chief of Police/Chief of Police. For example, you can grind your ass off and really go above and beyond to be a great cop and then be almost perfect and get people talking about how much they like you as a cop and want you to be a senior and eventually you will get recognized or just be OS/friends with Deputy Chief of Police/Chief of Police. If you are OS you can join any channel. Like the conference room where most of Sr. APD go to play cop. You can also join any other channel and it’s easy to become friends with the Sr. APD because you can talk to them whenever you want. Bringing me back to my last point that if you are friends with them you can play with them as much as you want. Basically get to cut to the front of the line and play with them as much as you want. Goodman even said it himself that he was glad he got OS because he knew it would better his chances of getting Sgt. It's a major perk.
Overall have a good rep and be friends with some higher ups and maybe apply for OS and you'll do fine. This might be common knowledge for some but it might not be for others.
As for the rest of the ranks I have no idea because they are usually kept behind closed doors.
So these are my opinions overall it might help someone. It might not but these are just from what I experience. If you got any questions just ask me. Peace.