I normally like to put the new kitty in a cat crate (those two teired ones), in a room that I know that the other kitties frequent.
In my current apartment, that room is my furnace room; the cat litter boxes are in there on one wall, as well as their food\\water on the opposite. When I introduced Kiira, I kept her in there for about a week; the other cats could see, hear, touch (through the kennel), and certainly smell her, without having the fear of being 'taken over' by an older cat. She's 2 1\\2, and everyone else was under a year.
After her 'confined' time, I put an extra litter pan, food, and water in our office, and put her in there; but I didn't shut the door...I let her go; she basically stayed in there for another 4 days, and then started venturing out more and more. She didn't have any real spats with anyone, except for Martha, who is our resident hissy princess. They didn't get along very well at all for a long time, but they weren't hurting each other; although it sounded like 'war' in the house at times! But it really was all noise...very little actual scuffles took place. After a while, when I knew Kiira knew where all the 'resident' litter pans were, I took up the office pan.
With Sable, because she was so young, I made her spend only a night in the big cage alone; after that, I put a litter pan in my living room (as that is where she spent much of her time, and we all know baby kitties...they hold it till the last minute!)
Sable adjusted super fast, and there were no actual scuffles when she came into our home; she did 'beat up' the baby kitties though when ever she had the chance...Lol!
So, yeah...it can vary, how the actual 'introductions' go, but I have never really done much differently than I have listed; I do know, the more you try to get in the way (protecting one, or disciplining another) the longer it will actually take for them to adjust to each other's companionship...stay out of the way, and before you know it, they will all be snuggled in together; it may take longer than you would like, but it will happen.
I don't think it's necessary to 'shut' everyone in separate rooms (or new one in one room, other one's free...the 'old ones' still know he's there...him 'hiding' makes things more stressful and they get more anxious to meet him!), like some may suggest; not that they are wrong, but if you are trying to prevent stress from protecting turf, don't 'give' each cat separate turf to protect...it just makes the whole process longer than it really needs to be. JMHO...take it with a grain of salt!
The kennel idea still keeps them separate, but the cat is immediately able to start getting used to his new surroundings, without being too overloaded by them, and your cats can immediately begin sorting him out, but can freely leave the room if they wish.