Wah How to use If I were you,...

We can use this expression If I were you, ... to give suggestions. In fact this is the first part of a second conditional form. 
(See more in Wah How to use second conditional..)

    If I were you, I would consult a specialist. ( = I think you should consult a specialist.)
Or you could say 
    I would consult a specialist if I were you.
because they are normally reversible.

Note: We usually use were in formal English, even when the subject is I,he,she,it. 
           But in informal English was is acceptable with these subjects. 

    A: I forgot my umbrella in the hospital. 
    B: If I were you, I would phone the hospital right now. 

    A: I always forget things easily.
    B: If I were you, I would take a note.

    A: I feel terribly drowsy in the office.
    B: I would get some coffee if I were you.

In spoken English, we can use If I were in your shoes, ... instead of If I were you, ... especially when the person receiving the advice is in a uncomfortable or difficult situation.

    A: I saw my boss, who is married, kissing his secretary, who is not.
    B: If I were in your shoes, I'd keep my mouth shut.

    A: I found a wallet at the park with a lot of money in it.
    B: If I were in your shoes, I would call the police.

    A: I have had a terrible headache for a week.
    B: If I were in you shoes, I would see a doctor.

If I were you, I would take a break.