Always play a game well planned and don't have a fear for your opponent because it can lead to blunder mistakes and look around after every move of your opponent.
Yes, to have fear does not help at all as it does paralyze your logical thinking process. You make fearful moves and weaken your position even further.
You do not attack when your position requires it and lose the initiative and then his superior positional knowledge will come into effect and he will slowly but surely grind you down and beat you.
After all, if the difference in rating is not too high, you can still beat a stronger opponent if you play above your level in the particular game and if he is in a bad playing mood himself on this day.