How to use だんだん properly?

Question

If I wanted to say, "Ken's getting better and better at Japanese", then would this be correct?

けんさんはだんだんじょうずになります。

Answer 1

Your usage of だんだん is just fine. It's a standalone adverb which can be used without any other particle. An adverb is usually placed just before what it modifies (in this case, じょうずになる).

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You have to use the progressive form of なります; otherwise the sentence would mean "Ken gets (or will get) better and better at Japanese".

けんさんはだんだん日本語【にほんご】が上手【じょうず】になっています。

To make this a bit more natural, you can add a subsidiary verb ～てくる and say:

けんさんはだんだん日本語が上手になってきています。