What Islam says about choosing a spouse

Someone close to me has her proposal coming but it is very confusing for her as to what to see in the potential person. Nowadays it is all 'show-off', one cannot decide how honest and true they are e.g. parent not telling about son job or temper in a job which becomes a problem in later life. What does Quran and hadith says how to/what to see in a spouse especially when it comes to marrying daughters or sisters