I am married, filing separately and my spouse is using standard deduction. How do I select standard deduction for myself?

TurboTax will default to the standard deduction.  Go through the filing status questions by going to My Info - enter Married for Marital Status and then go through the filing status questions.   When you select Married filing Separately, TurboTax will ask about your spouse's intentions.    TurboTax defaults to the standard deduction.   

And if you don't enter any itemized deductions like medical, charity, property tax, etc.  it will automatically give you the Standard Deduction.