This website has scripts for a lot of famous films.
Try reading scripts as you would a book. I read scripts where I'm very familiar with the film. If you read a lot of dialogue, you'll find writing dialogue easier.
RebelRogue, you gave some examples:
"Uhm... Hello" she said uncomfortably,while avoiding his eyes.
"H..h..hello" he stuttered,not expecting to see her there.
"Hello!" She said excitedly,her joyous energy filling up the whole room
The thing is that when you look at what they're saying, you then repeat it in the description. For instance, it's clear the middle one is stuttering; you've shown that in H..h..hello. It's clear "Hello!" is said by someone who's excited, because of the exclamation mark. I'd suggest using adverbs very sparingly, otherwise you'll end up with a Barbara Cartland type novel, eg:
"How dare you?" he said angrily.
"Who are you talking to?" she asked bitterly.
"You shouldn't have done that," he said resentfully.
And best (this one was from one of her novels I read when I was a teenager):
"I love you," he said lovingly.