Deadlifts for reps and losing a good bit of blubber around my midsection are probably the two biggest things I did. I didn't need any "advanced" tricks like chains, bands, paused lifts, ROM progression, etc. I'm not saying those methods don't work or are unnecessary, just that I didn't need them to hit 600.
Like @Vincepac1500 said, a lot of it is just mindset and making sure you're always striving to add weight to the bar and reps to your sets with any given weight.
I've also failed maybe two or three pulls at the most in my life. When I step up to the bar I know I'm going to lock it out. Its a given in my mind. Every single time. That barbell is going to move.