Large head size
One of the hardest parts of the game when starting up is timing your shots so that you contact the ball well. Having a racket with a larger head size makes this easier as it gives you an increased surface area to strike the ball with and a greater margin for error. The best beginner tennis rackets will usually have a bigger sweet-spot which is the place at the centre of the racket where you want to hit the ball for optimum impact.
Luckily, there are lots of rackets now that have big head sizes and generous sweet spots so you have plenty of choice. A large head size is especially important if you are a beginner as it will help you enjoy the game more and improve quicker. Once you get used to hitting balls over the net, you’ll like tennis more and more and can then look at progressing to a racket with a smaller head size.