[Barone1551]

Ok I will attempt to help, but I will say that I do not consider myself an expert, and if someone like Ronin, MMM, ect come in and make corections, they are the ones to listen too.

The second part of my second sentence could be wrong, I am unsure how to spell it since I have only heard the phrase verbally. So for now just ignore it. When I learned じょうず (skilled at),　I learned いたい (pain)　and 好き (like) along side it. We used が　for all of them. The way I understand it is you dont use は　becuase it is not the subject. If you would extend the sentence it would be : あなたは日本語がじょうずです。

So the subject would be あなた　(you). Again this is my understanding.