I've been wondering about this one for a while, also when Nila was coming to live with me and the two cats I had at the time.

So I wonder how you people with cats have gone about this.

Thing being, advice is to keep them separate at first. New kitten in its own room. Then get it in the living room when the other one isn't there so it can sniff around and get accustomed to it and the scent of the other cat.
Then after that bring it back to its own room, certainly when the "old" cat is returning.

The other thing... pet the kitten with a cloth and leave that in the living room so the 'old' cat can get used to the scent and explore it at her own leisure. Meaning not putting it in her basket or rubbing it over her.

Then gently, if that all goes well, get them closer together so they can hear/smell the other but not yet see one another.
That would then be the next step, and keeping that meeting very short after which the kitten goes to its own room again.

PROBLEM with that:
It all sounds great, theoretically. But... it means I'm going to get a well socialised kitten that I then keep in a room all by her lonesome self.
I do not think that's healthy. Poor thing still very young, away from mum and siblings to sit in a room by herself.

So how the heck do you go about this?
My niece, a cat lover who always has had many cats, introduced many new ones as well, says to just introduce them, pet them, play with them, give them lots of attention but more so the 'old' one. A bit of cat-sweet so they can nibble together, at respectful distance.
But not all that fuzz with the separate room.

Now that would be best in the sense that the kitten doesn't spend maybe days mostly on her own (poor thing!!!) but I can imagine it increases the risk of it not working out...

Experience from you guys?
How have you gone about such things?
And did it work out well?