The basic difference is that 'let's get started' is right, and 'let's get starting' is wrong, it's not possible. Get on与get in的区别为：意思不同、用法不同、侧重点不同。 一、意思不同 1、get on：（同…）和睦相处，继续做。 2、get in：当选，挤出时间做。 二、用法不同 1、get on：get是英语中使用最广泛的. The problem is (i think!) that let's get + ~ing implies duration.
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