Furnishings should be neutral. Because you like a certain colour does not mean someone else will. Walls should be kept to magnolia or white, making them easier to paint over at the end of each tenancy. There is a fine balance to be struck between the cost of furnishings and their attractiveness, but they should be of a sufficiently high quality to provide a decent rental yield.
It is also worth bearing in mind exactly what a tenant will want, or what he or she will demand. This could include anything from a microwave to a second phone line for the Internet. Standard requests from tenants may vary from area to area, and students in particular may have different requests to general tenants.
Specific furnishing may make a house more valuable and attractive to tenants. One example of this is wooden floors. However, it is always worth remembering the cost of upkeep before outlaying too much money. A letting agent should be able to provide you with an inventory.