Kittens are very social creatures, and require playmates. These can include other kittens, other cats in the home, dogs in the home, and you. If you do not have any other pets for your kitten to play with, be prepared to spend at least a few hours each and every day playing with your kitten. If you do not have the time to do this, then you may want to consider getting another kitten so they have someone else to play with.
Kittens also learn manners from each other and from other cats. Kittens will play rough, and only by disciplining each other, will they learn how far is too far to go, which can help immensely in preventing behavior issues as adults. Even other adult cats in the home may unwillingly help to teach your new kitten manners by smacking them down when they are too rambunctious. Kittens will also follow the lead of other cats in the home, and will learn rules and things like litter box use from them.
If getting another kitten or pet is not feasible, there are still things you can do to increase their socialization. Kittens are most open to socializing with other cats between 6-12 weeks of age. After that, they become less and less open to socializing, but it can still be done. If you have any friends or family with kittens, have play dates. Schedule regular times when your kittens are still young to come over and play with each other. This will help immensely in increasing your kitten's socialization skills and manners. Kitten Kindy, which is a training class for kittens, is also an option if you have it available in your area.
It is also good to socialize your kitten with new people. Take your kitten with you to pet stores that allow it. If you have friends or family coming over, entice your kitten to come out and play with them. The more your kitten can be around unfamiliar people and situations in a positive manner when they are very young, the better they will be to take places when they are adults.
A normal healthy kitten should have two speeds. Play hard and sleep hard. If your kitten is not very playful, or sleeps most of the time, then there may be a medical issue and you may want to take your kitten to the vet to have them checked out. Some kittens can be more introverted, but even they should enjoy play for several hours each and every day.