Quick Answer: It depends.
A character’s inner thoughts are generally written in italics without quotation marks.
A few examples:
Max crept down the hallway and into the bathroom. He checked the drawers in the vanity. Where did she keep her pain medication?
However, italics are not required.
As I moved closer and pursed my lips, I closed my eyes. As a result, my kiss landed on her upper lip and nostrils. Oh my God! How could I miss so badly? I tried to adjust but she pulled away.
However, If you present the thoughts as an inner conversation, then the thoughts can be written like dialogue (with quotation marks), using dialogue tags to indicate the words are inner thoughts and not actually verbalized.
For example:
“I can do this,” Yvette thought, “If I pace myself, I can make it all the way without stopping.”
Personally, I never use the second option. I believe this makes it too easy for readers to mistake the inner dialogue for spoken words.
