routine changes?

Ok, so everyone talks about changing up  your routine every now & again so your body doesn't just get used to it and stop increasing.
 
What exactly does this entail - as in, WHAT specifically should change?
 
lets say, you're doing a 3 x 8 routine, focusing on the major compounds:
 
bench
pullup
oh press
deadlift or squat, alternating workouts
 
So, what should you change up?  the order?  the number of reps?  How often should you change - every workout, every 8 weeks, what?  What do you change your squat? your pullup?  your oh press?
 
p.s.  finally got a rack for my home, so able to do barbell bench & squat, not just the dumbbell I've been doing since I started about 13 months ago.

changing up your routine can be anything.

it can be as simple as after your deloading and you can get into periodization. Same program.

or you can change your exercises, reps/sets, super sets, rest time, rep speed.

or you can change the whole program. Which is probably good to at least do a few times a year.

6'3"  @213

Squat 1x20x275

press:200, Deadlift:475, Bench:300, P.clean:235, Squat:385

"The only failure that is final is to stop trying to improve"