While this requires some investment, I've found that having a good broadcast monitoring solution helps a lot during online calls. Whether you're on headphones, in-ears, or using a full wedge, having your own voice echoing back at you allows you to easily know if you're speaking clearly at the correct volume. You can also tell if you're backing away from the mic, whether background noise is audible on the far side, and so on.

Professional public speakers and radio personalities monitor themselves, so why shouldn't you?

A cheap analog mixer or audio interface will let you do this, and obviously the sky's the limit if you want a full digital mixer with DSP and all the bells and whistles. There are software options but the latency can be jarring if you aren't used to it.