We have a cat that was born and lived in our house 13 years ago, she is very domestic, never goes outside the house, and thus, other than her mother that passed away 3 years ago, have seen no other cats. We adopted a baby kitten, and waiting for he to get old enough before bringing her to our home, she is still nursing with her mother. What are things that we can do to make our cat accept the newcomer.
There are plenty of other answers addressing how to introduce cats to each other. Browse those questions and get some ideas, but I'd like to address what will probably be the main issue in this specific case: Kittens are devilish, hyper hellions.
Your older cat is probably used to a pretty relaxed lifestyle, free from disruption and stress. Introducing a kitten into the household is going to change that. Here's what you can do to keep everyone happy:
Give your older cat a safe, calm place to relax in. A little nook behind/on top of furniture, under a bed, somewhere she can get away from everyone else. Additionally, make sure you exercise the kitten, a lot. A tired kitten will be less likely to annoy your older cat. Get some cat toys ("fishing pole" type toys are great, you can run the cat up and down the stairs with them and tire them out quickly) and keep her hunting/playing instincts satisfied by the toys rather than your older cat (who probably won't appreciate claws in her tail). Remember that cats are "sprinters," when they hunt, they go hard and get tired quickly. Multiple short playtimes will be more effective than one marathon.
Best of luck with your new family member. Don't forget to add an extra litterbox to your house to help avoid disputes as well.
Actually, there is a way to prepare your cat for bringing a newbie. I help homeless cats so sometimes I have the same problem - how to put my domestic cats in touch with the new ones.
Smells play the greatest role in cat's life. Take a toy or a plaid or a bowl or even a litter box of a new cat and bring it to your old one. He/she must to get used to its smell. When your little one comes, his smell will be familiar to your cat and less stressful.
The second step is the day of their meeting. Don't put them in touch at first second. Put the new one in a closed room, but let your old cat stay free. He is at home, it's his territory: he's been living here for all his life and has all rights. He must get used to sounds that the new one makes, to his presence. If the old one isn't aggressive, you can open the door in a few hours. They both might hiss at first time and mew aggressively. But it's a natural behavour. If you are afraid, you might cut their claws so they don't hurt each other if they want to find out who's stronger.
Don't let the new one eat from the old one's dish, play with his toys or sleep in his favourite places. Your old cat must feel safe in his house. Touch him, stroke him, love him. Don't show him that he is replaced with the new one, that there is another favourite child.
But at the same time play with the new one in order he not disturb the old one, and stroke him as well. He also needs to feel your love. At first you may leave them in different rooms when you leave the house. But sooner or later, I am sure, they will become friends. It may take some time, but not forever :)
Good luck :)