take up doing开始做;开始做某事
set out on doing 着手做，
意思是一样的，用法区别：take up是口语用法，相对比较随意，set out on是书面语用法，相对比较正规；
举例一：
Remember, the best mentors are busy people, and they may be opposed to someone trying to take up a lot of their time.
切记，最优秀的导师通常都非常忙碌，所以，如果有人占用他们太多的时间，肯定会引起他们的反感。
举例二：
I know how busy you must be and naturally I wouldn't want to take up too much of your time.
我知道您肯定特别忙，我当然不想占用您太多的时间。
举例三：
He got up at four and set out on foot to hunt black grouse.
他4点钟起了床，徒步出发去猎杀黑琴鸡。
举例四：
Four of the most powerful men in Russia set out on a top-secret mission.
俄罗斯最有势力的四个人身怀绝密任务出发了。
