It is recommended to connect a few minutes early to make sure that everything is working ok. Once the class has started, it would be difficult for me to answer your messages outside of Zoom. 

You need to have a good internet connection to make sure that there are no bugs with the video or the sound. You can test your internet on speedtest.net 

If there's a lag between the sound and the video, it is recommended to close Zoom and reopen it. That generally fixes the lag. 

If that does not fix the issue, you can turn your wifi on and off. 

A small lag is normal. 

To have the best experience possible, I suggest connecting the internet directly to your computer with a cable if you can. If not, you need to stay close to your router. 

If other people in the house are using the internet, it would be best to ask them not to while you take the class especially if they are doing things like watching Netflix (uses a lot of Internet). 

Close all other applications and programs on your computer, smartphone or tablet. 

You can connect your computer to an external speaker for a better quality of sound, ideally with an aux cable. There might be a delay between the sound and the video if you connect it by bluetooth.