Golf is certainly a game of concentration, but that does not mean that you should be tense when you hit the ball. Staying relaxed through your swing will keep a fluid motion and help you to swing through the ball. Often amateur players will have issues with getting the ball up in the air, to combat this they overcompensate by swinging upward and essentially trying to lift the ball. This is in fact the opposite of what they should be doing. Hitting down and through the ball will allow the natural loft of the club to lift the ball and result in improved flight.
Let your club to the work when it comes to getting the ball airborne! Golf club technology has improved exponentially over the last few decades and made the game much more friendly to beginners. Focus on a smooth motion and solid contact, the rest will take care of itself!