Maximizing personal business deductions

Hi, my wife is a CRNA that works for a large hospital. She is planning on starting an LLC as an anesthesia provider in order to make additional money outside of her current job.

 

What kinds of things can we write off as business expenses? Eg car, gas, computer, internet etc 

 

What should be keeping track of if she is starting the LLC later in the year?

 

Can we include deductions before the LLC was created or only after it was created?