"get rid of "一般指"处理(掉) / 除去", 其对象多为手头待解决的或者无用的东西;而"shake off"可理解为"暂时丢置一旁,不去理会,但是并没有处理"'.

it depends in what kind of sentence they are used. Get rid of it is mostly used in anger or when you wane loose something negative. Just get rid of it, they say. For example; get rid of that dog, it is biting my shoes again. Shake it off is mostly used for something you figuratively speak of. So for example; I got a really bad feeling about this. Just do it, shake it off. With other words stop feeling that way. I hope this helped, good luck :)

"get rid of" - throw away like rubbish. If you get rid of something, you never expect to see it again. "shake off" - get away from, leave behind you. They are different, but phrasal verbs like these often have different meaning depending on their context.