To get a better connection, you may move your router closer to your TV or adjust the position of your Chromecast device.
If you wish to connect your Chromecast without using Wi-Fi and you have an available Ethernet connection nearby, you might benefit from using the Ethernet adapter.
If you have the option of to use a wired connection, or if you have a dual-band Wi-Fi router and can use 5 GHz on your computer, this may yield better performance. Note that your Chromecast must be already set up and connected to your Wi-Fi network, and AP Isolation or Client Isolation mode must be turned off on your router.
Other apps such as streaming and media apps and devices on your network may be reducing available bandwidth. Minimizing these may help.