The only thing you need to change is the word order. In Spanish, it's more natural to say:
"Por favor, quiero un tequila más."
Here's why:
* "Por favor" (please) usually goes at the beginning of a polite request.
* "Quiero" (I want) comes next.
* "Un tequila más" (one more tequila) completes the sentence.
So, the full and correct sentence is: "Por favor, quiero un tequila más."