I have a scene where my character has to feel scared, sad and alone. I'm good at describing her surrounding but describing feeling are a bit harder for me. I also have scene where she has to be heartbroken but I feel like it sound stiff and simple.
Hemmingway has some solid advice (tip 5). Don't describe the emotion, describe the thing that caused the emotion.
Imagine a young couple, expecting their first child, and suffering a miscarriage. It's probably very difficult to describe accurately what that feels like, but even if you succeeded, it wouldn't make the reader actually feel it. If, however, you describe the sequence of events that caused the emotion: sudden stomach pains, the husband rushing to the hospital, waiting for hours to see the doctor, all that tension will induce emotion in the reader without you ever describing what anything feels like.
It's events that make readers feel, not descriptions of emotions.
The further you trace the events back, the more you layer the emotion. Contrast the shock of the miscarriage by showing the joy of a successful pregnancy. Of course, don't describe the joy, show the difficulty in getting pregnant, and then release that tension. Go back further, why does becoming a parent mean so much to both of them? The further back you go, the bigger the payoff.
Well, to be honest, this is a perfect example where you want to show how the character is feeling. So have a thinking about what your character is doing in response to this heartbreak and insert this into the scene.
Like, I have a character in my novel, in one part, she is nervous when she is ambushed (quite by accident) by another character at a quiet moment, so I relay this in her behaviour. Fidgeting with her fingers, deliberately moving out of this person's way, hesitating to follow, walking but with distance.
So how does that heartbreak manifest? Is she crying? If so, what sort of crying is it - overwhelming, thick and fast tears? Or is she feeling numb? Can you show that by her not hearing what another character might say to her, or just aimless gazing out a window?
This isn't a comprehensive list of what you can do, but the emotions will show as you show what is going on.
If you are willing to be mean to yourself, maybe listen to sad songs, or read sad things, or tap into past memories of when you felt sad/heartbroken yourself (this applies to any emotion). Remember how your body responded then. Maybe, if you get involved enough, you'll feel reactions during the exercise (if you can even call it that). Then you can incorporate those into your writing.
Also, we all know that cliches and very overused tropes sound stiff and simple. They pull readers out of the story and make them go "Aha! There's that thing again! The author is trying to display _____!" So avoid using those kinds of things that you've seen a lot before, I guess.