Paint:
If you are lucky to have windows in your hallway, you could leave it white or very neutral, but the moment an entrance because dark and only illuminated by artificial light, new color on the walls can give it interest and warmth. With a small hallway, you could go extra dark, to seem the adjoining rooms look more prominent, but I wouldn't do that in a long corridor, Instead choose a light neutral color that is cozy and interesting, like a taupe, mauve or a blue-grey.
Lay down a long rug.
It is such a beautiful look. When I first saw our old house, the owners had rugs only in the hallways, and it made the house look so lively. The thing about a rug in a hall or corridor is that because there isn't a lot of furniture, it grabs all the attention, so make it a great one.
Pictures.
This is the perfect spot for family pictures, and walking along it will make you happy every single time.
A Vignette.
If there's a wall at either side, use it to hang a painting, put a table and vase with some flowers. It is a lovely way of using what would be otherwise an empty space. Get more inspiration on my Pinterest board.
The starter pack for your hallway:
1. A wooden bench or French console table
2. a rug
3. A sculptural lamp
4. Wall art
5. A vase
6. Picture Frames