to shoot at one particular person, animal, or vehicle that you have chosen from a group

The snipers picked the soldiers off one by one as they ran for cover. 士兵们慌忙走避时，狙击手们将他们逐个击毙。

to take the best person or thing from a group

It is relatively easy for newcomers to pick off the most lucrative business and ignore the rest. 新来人员较易挑选最有利润的业务而忽略其他业务。