To describe something that tend to happen with great chances, but we couldn’t or wouldn’t guarantee there’s 100% sure. We may use mostly, in general, or generally speaking to moderate our wording in a safer way.
They’re mostly good people, although they have made a few mistakes.
Tom and Scott are good lawyers in general, although they left the firm with noises.
We may also use them to begin with a sentence.
Mostly, the automobiles produced by Toyota are economical and reliable.
The following sentence that tries to emphasize the probability is incorrect.
In generally speaking, ….
The correct ways to express are as these.
In general, I’m satisfied with the insurance company, they responded to my claim of a car accident quickly and firmly.
Generally speaking, vehicle insurances are necessary to drivers.