One of the simplest ways is just to be firm with a spirit and tell them to get lost - this does work on many occasions. You are just making it clear to them that there presence is not welcome in your space.
You could also recite some prayers or affirmations that give you strength and courage. Most spirits are not harmful, many just want attention, but they can be intrusive probably without really meaning to.
For longer term there are mediations and cleansings for psychic protection of yourself and your home - these are very simple and very safe. If you follow a main religion such as Christianity I'm sure your local priest or minister would carry out a house blessing if you feel this would help.
If the 'spirit' is a ghost - they are not the same thing - then you have nothing to worry about since a ghost is just a play back , like a supernatural dvd, and can't hurt or interact with you and you don't need protection. Lots of luck.