Check that your hardware and software meet Genymotion Desktop minimum requirements. Please refer to Genymotion Desktop Requirements.
If you are using developer tools, make sure that you set Genymotion Desktop to use the same SDK tools as your IDE. Please refer to Configuring ADB.
Virtual Device Android version and density have a huge impact on performance. If Genymotion Desktop is too slow on your computer, try a virtual device with a lower Android version and 320-XHDPI density.
If you are running Genymotion Desktop on a laptop, make sure to set your power settings to performance mode. Also, some laptops have dual GPUs (Intel and NVidia/AMD). Make sure that Genymotion Desktop runs with the high-profile GPU (usually AMD or Nvidia) instead of low-profile (usually Intel).