As you're writing, you cannot communicate to the reader what a character is feeling unless you can feel it. It's that simple.

I was writing a scene last night where a woman suddenly feels a hand covering her mouth. She knows her friend is in the house but not if it is him or not. How do I describe this?

I closed my eyes and envisioned the suddenly darkened room. I waited until I could feel my heart beat faster as I was blind and vulnerable. I noted how all my senses went into overdrive. I could smell things I could smell before. I could hear things that may or may not have been real.

I then imagined the hand suddenly covering my mouth. I felt the panic. I felt the fear. I felt the strong arm and hand.

I had my description for my character.

How do you get the right descriptions for your character?