Having your camera, you will definitely take photos of your friends, relatives either during the parties, trips or meetings. One of the prerequisites for good portraits (assuming that you are close) is fast portrait lenses. On DX camera (crop sensor) it would be around 50mm lenses, on FX (full frame) - around 85mm. Lenses must be fast - in general, I noticed that rather usable aperture from my point of view is f/2.2-f/2.8 - it has sufficient depth of field, and background is well isolated. Keep in mind, that shooting more than one person they will have to be in the same distance from you as one of them will be blurry. Otherwise you need to step back and decrease aperture. If you want to shoot groups of people and even inside - 35mm or shorter lens is much more usable (and equivalent on FX or full frame sensor) but shorter and fast lenses are getting rather expensive here (Nikon though has very nice 35mm f/1.8 DX lenses - cheap and amazing; see my post on choosing lenses).
Going back to portraits - I have noticed that a lot of people take pictures of their friends and relatives while they are posing. In most cases - those pictures are kind of artificial, as too little people feel natural in front of camera. Better try to catch emotion. Take your camera with you and be invisible. Snap your photo when nobody is expecting that and even will not notice that. You will see - your portraits will be way better and stronger than posed ones, as people express their true emotion, not impersonated one.
Anyway, if you need a posed portrait - talk with your model, make him smile naturally, not just forcing him to say 'cheeeese' and get one more posed picture.