Qǐnɡ dàjiā zhùyì yíxià.
请大家注意一下。
May I have your attention, please?
Notes:
请(qǐnɡ): please
大家(dàjiā): everyone, you(plural)
注意(zhùyì): to pay attention
一下(yíxià): for a while
Example:
A:请大家注意一下。
Qǐnɡ dàjiā zhùyì yíxià.
May I have your attention, please?
B:好。
Hǎo.
Ok.