Make use of appliances that double as storage or counter space. This will include any appliances that are set to be installed under a counter or actually have a counter on top of them. In small kitchens, under-counter refrigerators and kitchen units combining both the oven and microwave into the same unit are great ways to save on space without sacrificing function.
Use shelving whenever possible. It goes without saying that making use of the vertical space in your kitchen can drastically increase the options for both storage and functionality. Placing a shelf over your stove, for example, can allow you to store your pans or spices or other commonly used items. For a spice rack, consider a wall mounted or in-wall option to make the best use of space with your kitchen units.
Use the smallest versions you can live with. While that micro refrigerator may be a great space saver, it is realistically not going to work for you. When shopping for appliances, be sure to take the functionality of the device into account just as much as you would the size. If it's too small to be useful, it's not going to give you any benefit.
Consider all-in-one kitchen units. While best served in extremely tight working conditions and the smallest kitchens, all in-one-kitchen units are available that combine a small sink, usually one or two burners, an under-counter refrigerator, as well as a small kitchen pantry. They usually come pre-assembled, so all you have to do is situate them, then hook them up to power and water.