Making a good first impression
Flight attendants are trying extremely hard to give the impression that they are competent yet approachable and warm. Several people are nervous about flying and hence flight attendants need to be comforting to them.
Seeing who is in their senses
Though not in Saudi and/or Muslim country airlines, other airlines and several airports offer passengers the chance to drink prior to their flight.
Some people tend to go overboard and the flight attendant will think about the best way to handle these types of passengers.
Evaluating your attitude
The flight attendants try their best to judge whether you have a withdrawn, helpful or belligerent attitude. There have been very few cases in which somebody was asked to exit the plane prior to take off.
Looking at the physique of the passengers
Those passengers who can be seen as physically strong or powerful are often seen as a good resource. If there is somebody who seems to be muscular, strong, or powerful, people often make a note of where they are sitting.
If any situation arises where these muscular people could be used, then the people remember where they are sitting. This may include helping unload overhead luggage, or to control a rude passenger. Weak passengers are not made to sit near emergency doors too.
Thinking about the language you speak (English)
As English has become the centralized language of the world, it is easier for everybody to communicate in that language. However not everybody can speak English, and if two people, who do not speak a common language, try to communicate, it will not end well. Hence somebody who knows 2 or more languages is preferred.
Checking if there are any other flight attendants or pilots on board
This is a very useful and important occurrence for the flight attendants on duty. In some cases, the flight attendants traveling with them will help them out in times of needs. The pilots can also help out the onboard pilots in case it is needed.
Looking to check your health
Passengers who look pale or deathly ill have been removed from flights numerous times before. Nobody wants an illness to travel with them in an enclosed space for a long duration of time.
Which of the passengers are attractive
Attendants may find some passengers cute, however in their personal lives, they would be too shy to say anything, but as an attendant, they can start small talk by going and saying hello.
Checking the size of the hand luggage
Flight attendants usually check the size of the luggage and often wonder how some people manage to get full sized luggage to put into the overhead containers.
Finally, their bed back home
And be it the start or end of the flight, they are definitely thinking about their bed back home, because really who isn’t thinking about their bed at any given time.