Can you say that you really tried?
Can you say that you did your best?
You have a good voice. (Should be: You have good voice.)
You have a good simile. (Should be: You have good smile.)
Are they grammatically correct?
I think that many (but not all) contexts would require "Can you say that you have really tried?"
Can you say that you did your best? CORRECT
You have a good voice. CORRECT
- (Should be: You have good voice.) NOT CORRECT
You have a good simile. CORRECT
- (Should be: You have good smile.) NOT CORRECT
It would also be possible to say
"You have the best voice in the choir."
"This is the good voice we have been searching for."
"Show me your good smile."
Except for some idiomatic expressions ("giving voice" for example), I think "voice" and "smile" always require an article (either "a" or "the") or an adjective ("Give me your famous smile.")
'You have a nice smile.' is far more likely to be said, at least in North America, when you mean that the person has an attractive smile.
'You have a good smile.' sounds like something that would be said in a medical setting. Maybe you had some facial paralysis and lost your normal smile. Later you recovered from the paralysis and the doctor comments that you have good smile, meaning that the function of your facial muscles has recoverd very well and you are now able to show a full smile.