I just introduced my kitten and adult cat last week and the tips I read on here helped SO much!
Basically you want to keep them separate for a week or so. Set up a small room for the kitten with food, litter box, bed, toys, etc.
When you bring the kitten home, go straight to that room - don't let the cats even sniff or see each other. They will sniff each other under the door.
After 3 or 4 days I opened the door a crack (1/2 inch) so they could touch noses. My older cat hissed and growled.
On the 6th day I switched rooms- the older cat went in the kitten room and kitten could run around the rest of my apartment and explore.
On the evening of the 7th day I spritzed a little perfume on each cat so they smelled the same. I slowly opened the door separating them and then went on the computer and ignored them- I stayed calm and quiet. They were fine. My adult cat hissed a couple times and that night they were both sleeping on the cat tree together!
I also had a Feliway plug on during the whole process.