General synonyms:
* Began
* Commenced
* Initiated
* Launched
* Opened
* Undertook
More specific synonyms:
* For actions: embarked, set out, went ahead, got going, kicked off, took the first step, set in motion
* For events: arose, developed, emerged, came about, sprang up, came into being
* For processes: activated, triggered, set in motion, brought about
* For engines: fired up, ignited, cranked up
* For journeys: departed, set off, left
* For businesses: founded, established, created, launched
* For relationships: began, formed, started up
* For conversations: began, opened, launched, initiated
Informal synonyms:
* Got going
* Hit the ground running
* Took off
* Jumped in
* Set to work
The best synonym for "started" depends on the context of the sentence. Consider the specific meaning you want to convey and choose the synonym that best fits.