“I” should be capitalized.

“If you were” is used when you are about to state something contrary to fact. If you mean that the person is NOT good looking and you wish he or she would be good looking, then leave out the word “a.” “A” is an article, a little adjective, that needs a noun. “Good looking” is also an adjective phrase. (technically an adverb and an adjective, but we don’t have to deal with that right now.) To be grammatically correct, there has to be a “what” after “looking” if you leave the “a” in place.

You can take “a” out, and then “good looking” becomes a predicate adjective phrase describing “you.”

“If” implied “then” (If this is so, then something else is going to happen or is going to be so).

More reasonably constructed sentences might be one of the following:

I wish you were good looking.

I wish that if you were good looking then I were also handsome.

If you were good looking, then I would be better looking.

The more I look at what you wrote, the more I see it as a veiled insult. If that isn’t what you intended, you might want to start over.

Is this something that you translated from another language? If it is, it could possible even say – I hope that you’re good looking. or something like, – I’m hoping that you’re pretty. (or good looking)

Good luck!