Parenthesis, Exponents, Multiplication & Division, Addition & Subtraction. In order from left to right. Multiplication then division which ever one comes first then, addition and subtraction which ever one comes first.

 Mnemonic:
PEMDAS

 Mnemonic:
"Please excuse my dear Aunt Sally"

 Mnemonic:
BEDMAS: Brackets (parenthesis), Exponents, Division & Multiplication, Addition & Subtraction