There's not one perfect mouse for gaming, it really depends on personal preference and how you like to hold your mouse. Some of the things to consider when choosing a gaming mouse are: size, weight, shape, grip style, and extra features like buttons and DPI (dots per inch) settings.
For a beginner, a good option might be a mouse with a few side buttons for quick access to weapon or action shortcuts. Also, consider a mouse with adjustable DPI settings so you can fine tune the mouse speed to your liking.
If you're really serious about gaming, it's worth investing in a higher-end mouse with features like a better polling rate, more customizable options, and a more solid build. These can range from $50 to over $100, but the quality is often worth the price!