Suzanne Collins wrote The Hunger Games from the first-person perspective—Katniss's, natch—and the filmmakers kept that POV. So while we occasionally stray away from our girl (usually to Caesar Flickerman with some handy exposition to let us know what's happening), we keep Katniss front and center the whole time. That means more than just keeping the camera focused on her. It means that the film never tells us anything that she doesn't know, and reveals certain things (like her surprise evaluation with a final score of 11) just as she learns them herself.
That applies to characters like Haymitch, too, who we never see before Katniss does, and to situations in the Games like the giant fire that drives her from her hiding place. Every time we cut away from her, it's to things we absolutely need to know, and things which she herself would either already know or which she could probably make an educated guess at.
The filmmakers stay away from voice-over narration and other obvious signs that we're seeing things from her perspective. The movie wants to get as close as possible to looking at this world through Katniss's eyes without actually sticking the camera behind her peepers.
It's a great decision.
Not only does it keep the spirit of the book alive, but it keeps us firmly on our heroine's side from first frame to last.