The righteous dream is from Allaah and the bad dream is from the devil, so if anyone sees something which pleases him/her, then he/she should only relate it to one whom he/she loves…
Summary of what to do upon having a bad dream:
■ Spit on your left three times. Spit: A form of spitting comprising mainly air with little spittle
■ Seek refuge in Allah from Shaytan and the evil of what you saw
■ Do not relate it to anyone
■ Turn and sleep on the opposite side to the one you were sleeping on previously.
■ Get up and pray if you so desire.
Source / Reference
Hisnul Muslim 101 & 111