Looking on the internet deeply has found these results:

I am not good in dancing. is the most popular phrase on the web.

I am not good at dancing. 17,300 results on the web	I am not good in dancing. 125,900 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
I am not good at schmozing. Suddenly you got really good at dancing. I am not good at choosing the people I hang out with. You have a great deal to offer and I am not sure I'm worthy of it, but for now let's just enjoy a good dinner and some dancing. Andy sings beautifully, and he's really good at dancing. I thought the main risk was it would just make me too good at dancing. Suddenly you got really good at dancing. I've just always been really good at dancing.	I thought the main risk was it would just make me too good at dancing. I've just always been really good at dancing. I am not good in mathematics but it must have more than 100 years. I looked a lot like an orangutan, our close cousins, or the Incredible Hulk. Not very good for ballroom dancing. You have to stop looping me into this stuff. I am not good in these situations. The heat is not good for the dancing. You have a great deal to offer and I am not sure I'm worthy of it, but for now let's just enjoy a good dinner and some dancing. Suddenly you got really good at dancing.

I am not good at dancing.

17,300 results on the web

I am not good in dancing.

125,900 results on the web

More popular!

I am not good at schmozing.
Suddenly you got really good at dancing.
I am not good at choosing the people I hang out with.
You have a great deal to offer and I am not sure I'm worthy of it, but for now let's just enjoy a good dinner and some dancing.
Andy sings beautifully, and he's really good at dancing.
I thought the main risk was it would just make me too good at dancing.
Suddenly you got really good at dancing.
I've just always been really good at dancing.

I thought the main risk was it would just make me too good at dancing.
I've just always been really good at dancing.
I am not good in mathematics but it must have more than 100 years.
I looked a lot like an orangutan, our close cousins, or the Incredible Hulk. Not very good for ballroom dancing.
You have to stop looping me into this stuff. I am not good in these situations.
The heat is not good for the dancing.
You have a great deal to offer and I am not sure I'm worthy of it, but for now let's just enjoy a good dinner and some dancing.
Suddenly you got really good at dancing.