Everyone who is afraid of flying experiences their anxiety in a very personal way, so it is impossible to provide a one-size-fits-all set of guidelines.
However, what I can tell you with certainty—and what will help you immensely—is this: do not be ashamed of how you feel! You are absolutely not alone; you aren't a "pathological case" or a laughingstock. If you look around while waiting to board, know that you are surrounded by dozens of other people in exactly the same boat!
Tell the Flight Attendant. When you step on board or at the first opportunity, let them know. You can make a joke about it or simply confess your unease calmly; there is nothing to be ashamed of. Most importantly, you’ll find that the crew, with all their experience, will do their best to put you at ease and will know how to "keep an eye on you" discreetly throughout the flight.
Trust me, a passenger who openly admits their apprehension is much more appreciated than one who awkwardly tries to hide it (and usually fails!).
DontWorryFlyHappy!