Phrase Request – Synonyms for ‘Nobody’s Perfect’

There are a few phrases that you can use, such as in place (of), instead (of) (also stead), to express the "doing something for somebody", depending on the context.

In any case, the phrase for someone doesn't have to mean that the person you do something for must be lazy. This, again, depends on the context. Compare:

He asked me to do his assignment for him.
I offered myself to do his assignment for him.

Here are some examples of in place (of), in someone's place, instead (of), and stead, I found on the web:

John came to help in place of Max, who was sick.
When the king's cloaked challenge is answered, Fluellen stands in place of him, representing him, and receiving the blow.
She knew she should not have sent him to work in her place tonight.
"O king, take my life instead of hers. Let me die in her place," he pleaded.
... it was Judas who was crucified instead of him, ...
... she had to ask their family doctor to prescribe instead of him making it available to begin with.
Take me instead! Not my boy!
The chairman spoke in her stead.
The marketing manager was ill and her deputy ran the meeting in her stead.

So, you can say any of these followings (choose wisely, register is important),

He asked me to do his assignment for him.
He asked me to do his assignment in place of him.
He asked me to do his assignment in his place.
He asked me to do his assignment instead.
He asked me to do his assignment instead of him.
He asked me to do his assignment instead of him doing it himself.
He asked me to do his assignment in his stead. (formal)

I'm a native speaker, and we use "get ready" in exactly the way you describe.

Even though we sometimes qualify the phrase by saying: Get ready for [some event], that "for" clause can be omitted when the listener already knows where we are going. In other words, although get ready can mean different things in different contexts, I can still usually say:

C'mon! We're leaving! You need to get ready!

and that will be understood to mean: put your shoes on, brush your teeth, comb your hair and look presentable, etc.

The precise meaning get ready will vary, depending on where we are going. So long as the hearer knows where we are going, I don't need to add the, say, for your piano practice. For example, I have teenagers at home, so, for me, it works very much like this:

10 or 15 years ago, though, whenever I said, "Let's get ready" to my wife, that always included "Make sure we have the diaper bag!"

You needn't worry about get ready being misconstrued to mean "brace yourself for some bad news" or "get into your starting blocks." Those are very specialized meanings that people wouldn't even think about, unless they were in a situation where that would be the meaning that makes the most sense.

For example, if you wanted your picture taken, and I was holding your camera, I might say, "Get ready..." – which doesn't mean, "go put on your shoes," or, "brace yourself for some bad news." It simply means, "Get ready, I'm going to snap the picture now" – so you should probably just give me your best smile.