Well, there are two separate problems here. One is describing the emotions of a POV character whose thoughts the reader can actually see; the other is describing the emotions of a character through their actions and expressions and maybe a POV character's personal conclusions about their feelings. These are really quite different.
To describe the emotions of a POV character, I find it pretty effective to describe the thoughts that occur to them as a result of this emotion, especially nonrational thoughts that would generally not occur to this character outside of a burst of emotion ("He was gripped with a powerful urge to strangle that woman"). You can sometimes just name the emotion directly, but that needs to be when the character is specifically conscious of the emotions they're feeling, and is a very ineffective way of invoking sympathy with the character in the reader, so avoid it if that's what you're going for.
For describing emotions without showing directly what the characters are thinking, you have to stick with describing their actions, speech and facial expressions and try to get what they're feeling across that way. Knowing some psychology helps. Facial expressions are obvious, but I prefer the way actions and speech can give emotions away: people in emotional distress speak and act differently than if they were perfectly relaxed. Also be aware that different people have different ways of dealing with their emotions. People who are scared don't just have a scared expression and say they're scared. There are often layers upon layers of coping mechanisms: people express one emotion in the form of another; people project feelings they're feeling onto others to avoid dealing with them themselves; people start excusing what they're feeling as being caused by something other than what it really is. Thought processes change: when you're scared, your thoughts can become jumbled and irrational. Think about how your characters cope with emotions and how they will show this, not always in the most straightforward and obvious ways. This applies to all characters, POV and non-POV; don't think your POV character's emotions are straightforward just because you can write out their thoughts.
Personal experience always helps, if you notice the sorts of things you do or that cross your mind when you're feeling a certain way. To take an example from my own experience, in chapter eight of Morphic, a character is dealing with the loss of his father. I've never lost a parent, or even a grandparent or anyone else especially close to me, but I've noticed that generally when it comes to death, what hits me the hardest, bizarrely, is to think of all the things that the person had planned to do and now never will. So therefore, that character cries for the first time when it occurs to him that his father was in the middle of a book and will never know how it ends, resulting in something that is hopefully a bit more realistic and crushing than just, "X was sad and cried because his father died and that's bad."