Formal:
* Приступать к работе (pristupat' k rabote) - This is the most literal translation and is suitable for formal settings.
* Начинать работать (nachinat' rabotat') - This means "to start working" and is also quite formal.
Informal:
* Браться за дело (brat'sya za delo) - This means "to take on the task" and is more informal.
* Заниматься делом (zanimat'sya delom) - This means "to get busy with work" and is also informal.
* Взяться за работу (vzyat'sya za rabotu) - Similar to "brat'sya za delo," this means "to get started on the work" and is informal.
Phrases:
* Пора браться за дело! (pora brat'sya za delo!) - This means "It's time to get to work!"
* Давайте работать! (davayte rabotat') - This means "Let's get to work!"
The best choice will depend on the context and your level of formality.