Root (with an app or computer program), then Busybox, then SafeStrap - or TWRP on a phone with a bootloader that can be unlocked. (The first thing I do is back up the stock rooted phone.)
From there on, it's a developer's mini-laptop - things like a terminal app, App Backup and Restore, Helium, ES File Manager, Total Commander, Swiftkey, Programmer's Keyboard, Mobile Odin if it's a Samsung that will run it, Avast, Open Camera ... (I normally end up with about 100 downloaded [or installed from backup, actually] apps before I start using the phone.)