Depression in a friend or family member can be a tricky situation to contend with, since it often leads to social withdrawal. Your depressed loved one will likely avoid activities she previously enjoyed. She'll lack the energy to do much of anything. She might not be sleeping well. She might be consumed by depressive thoughts, and very likely will have difficulty motivating herself to do anything, be it the tasks she needs to complete for her job, her household duties or fun activities. You can help her by supplying her with some of the motivation she is lacking.
Educate yourself about depression, especially about the sufferer's propensity to become withdrawn and inactive. In addition, evaluate your relationship with your friend or family member. Think over past episodes where one of you cheered the other up. Consider what effect your input generally has and try to estimate what effect it will have now that your friend is depressed. If she usually responds well to your suggestions, and if she herself likes to encourage you in turn, your verbal encouragement is likely to have some positive effect even in her current state. If she tends to get annoyed at such suggestions, concentrate more on activities and less on verbal suggestions.
Do things together. If this is a friend, help him keep his house nice and pleasant. Open the windows to let air in. Get him to throw his clothes in the laundry. Help him fold his clothes if necessary. If this is a family member who lives with you, encourage him to do the chores with you. The goal is to get him active while at the same time keeping the environment habitable. Sit and watch TV or a DVD together. Even a depressed person usually can come out of his shell for a while, and talk and laugh a bit. Play a board game or a video game together. Even if he doesn't seem to enjoy it nearly as much as he normally would, doing just a bit is better than doing nothing. Listen to him talk about his troubles if he needs to. The feeling of having someone on his side will relieve some of his burden, and as a result he'll feel more energetic and more capable of getting up and getting things done.
Get her outdoors. If you live in the same household, encourage her to get out of bed, make breakfast for the two of you and announce you're both going for a walk. If it's a friend, go over to her house and take her for a walk. If you call her up, she might refuse to do anything, but if you show up at her house, it will be harder for her to refuse. Go to the beach together. Walk a bit, then sit and watch the ocean if your friend is too depressed to walk much. Drive somewhere nice and look at the view. Try to include at least a short walk if possible. Don't hesitate to cajole her a bit into activity--she'll likely appreciate the effort even if she shows some resistance.
Don't push too much. Don't get irritated if she doesn't follow your advice.
If you feel the situation is beyond your capabilities as a friend, don't hesitate to call for professional help.