I go big when I do rotational play so I use mods to stop culling and to make it easier to play the way I like. (MCCC & Slice of Life are my must-haves)
I delete every sim in the beginning - yes, even the townies - and fill all the towns with my own single sims. Yes, it does take a really long time. But, I use custom content and I really don't like how my creations look amongst the other sims, so it's a necessary pain.
I tend to go 4 sim weeks per household. But, it totally depends on how their household is going. Does the sim have a job? Are they making enough money to support themselves? If not, I'll play with them until they're living comfortably. Is the sim in university? Are they getting good enough grades? If not, I'll play with them and help them to get their grades up. Is the sim lonely? I'll help them find love. Do they want to have a family? I'll help them along. If the sim is doing fine - i'll just check up on them every once in awhile.
I will play with the same "world" for months and will get plenty of fun out of it. I do have a save file titled "beginning" just in case I want to start all over with the sims I've placed in the game. Sometimes starting all over is refreshing!
Variety is something that I really struggle with doing on my own, so that's where the slice of life mod helps out. It randomizes jobs, skills, friends, etc. and makes sure that I don't stick to the "same old" stuff. MCCC helps me to randomize marriages and pregnancies so that my sims are not always single and childless. I put it on a lower % so it will take some time for any of this to happen.
All-in-all, playing rotational is lots of fun! But, it takes a lot of patience and a lot of dedication to make sure your households are happy (or not happy, if that's what you're going for) and it can be quite the challenge, especially if you play vanilla.