It's easy to show hesitance, fear or angst, you can have a character smoking 5-10 cigarettes in a row, linger for way too long, act out, or something like that. But how can you show a character that is feeling great, has a lot of confidence?
My character is setting sail in a boat on its way out of a harbor (no pirates and no fantasy, just a regular dude in a regular harbor). The best I've come up with is looking at the horizon and smiling but I think it feels a little bit forced.
Think back to when you began a journey. When you began something new. Maybe it was moving out of your parents house and you got into the moving truck, ready to drive off for the first time. Maybe it was the first time you went on a trip with a group of friends or by yourself. Remember the feelings you had. The swelling of pride, eager for adventure and something new, free from the shackles of life. Feeling good isn't just a matter of having a smile. Many people smile even when they are sad or are in pain. It is an emotional state. You may also want to watch your prose too in situations like this.
Attach the emotions to actions. As he loads the boat with his belongings for the trip, does he quickly toss his bags into his cabin eager to get started? Or does he just simply prepare the boat for departure? Does he skip around and whistle his favorite sailing tune while making preparations? Or does he just walk up to the boat and prepare to depart? Is he able to sleep the night before? Most times people can't sleep on the eve of doing something they are excited or nervous about.
You don't need to write a long, descriptive, prose-filled passage to show he is happy or feeling great about the trip. You can do this throughout the hours leading up to the trip by expressing emotions and happy actions that he is doing while getting ready.
I'm going to disagree with the other answerers to some extent: I don't think it's true that actions / gestures / expressions are the best way of conveying a character's emotions. These things can convey that the character is feeling a certain way but they do a poor job of conveying those feelings. Lyric poetry is a really good example of how to do this. As a random example take Kevin Young's "Crowning" about the birth. Some of the techniques are particular to poetry but I think there are mechanics we can learn from this piece that translate to prose
Part of an effective lyric voice is fluid mixing of inner life and experience, achieved here with metaphors mixed with observation "animal smell / and peat, breath and sweat / and mulch-matter" to judgement and values included with report "driven / by mother's body, by her will / and brilliance". If you are writing in a conservative, 3rd person (limited) omniscient, you can still achieve some of this by being careful in what details you choose to pick, e.g. in this poem with the great closing lines "warming now, now opening / your eyes midnight / blue in the blue-black dawn." (To drive my point home: notice that the poem gives you no information about the character's body or expression and yet we know very clearly what the narrator is feeling in these moments.)
Applied to this case, I think the best way to show the excitement and confidence of this character is to detail his experience in a way that makes this evident: an excited person will notice how the light plays over the surface of the water, will appreciate the splash of an anchor being hoisted, will notice the school of fish darting to the surface before sinking away, will experience the sway of the boat as lively, etc. etc.
To soapbox a bit before wrapping, some writers today are a little too indebted to the screen. With actors and cameras, expressions and behavior are absolutely crucial in conveying the emotion of an experience. These tools though translate clumsily to writing -- it is telling that we often have to invoke an emotion to describe an expression (e.g. "beamed with excitement") -- and we have had much better native tools for eons.
In addition to what others have said…
If you're in that character's viewpoint, you can sometimeds show feelings with the choice and sound of words and the rhythm and lengths of sentences.
Here is an example from Audrey Niffenegger's The Time Traveler's Wife. Just before this moment, Clare has bumped into Henry in the library. She's met him many times, but he's never met her. (It's a time-travel thing.) Clare asks Henry out to dinner. Then comes this astounding sentence:
We plan to meet tonight at a nearby Thai restaurant, all the while under the amused gaze of the women behind the desk, and I leave, forgetting about Kelmscott and Chaucer and floating down the marble stairs, through the lobby and out into the October Chicago sun, running across the park scattering small dogs and squirrels, whooping and rejoicing.
She never explicitly says how she's feeling, but you have any doubt about what she's feeling at that moment?
You use the full narrative pallet that the novel form makes available to you. Different emotions manifest themselves in different ways. Some are very overt, some and entirely hidden from external view. Don't worry about doctrinaire interpretation of show vs tell; Use whatever techniques are useful in conveying to the reader.
If you want a brilliant example of how to show that a character is feeling amazing, I can think of none better than the description of Mole at the beginning of Wind in the Willows: https://www.gutenberg.org/files/289/289-h/289-h.htm#link2H_4_0001
It sounds like you may need to delve a little deeper into the character's internal life.
A common way to tell a story is to focus on the surface elements - what the characters say and do but in written literature, we have access to the inner thought life of the person.
Feeling a certain way is not just the moment and the actions but the history and context, the inner life, the sensations, and your subjective reaction to them all.
It may be of benefit for you to review Stanislavski's An Actor Prepares. In case you have not the time or motivation to read it right now (you should), let me give you a very truncated lesson as applied to writing.
Remember when you felt amazing (or whatever you need to convey).
What thoughts were going through your head?
How did it change your perception of the world around you?
What was the context of that moment?
Now, using words alone, make me feel it too. If you can do that you will portray the emotion of the moment vividly enough that the scene will come to life for the reader. There is no right or wrong way to show that feeling just so long as you make me feel it.
I hate to state the obvious but you could simply say it in the narrative. Not everything needs to be SHOWN. You may TELL one thing whilst showing another.
For the first the first time in a long time Bob looked to the future with delightful enthusiasm. He smiled. "Expiali - effing - docious!
For the first the first time in a long time Bob looked to the future with delightful enthusiasm. With a wry smile he untethered the rope and looked out over the horizon. Now was his time. "To infinity and beyond!"
So I've thrown in a couple of cheap pop-culture references but they contribute to Bob's characterisation. There are 30 years between the two references. Is he reliving his childhood? May be its something he picked up from his grandkids?
If it fits with the rest of your writing, one way is music. You have to make it fairly pervasive to do it this way.
The Black Tide Rising books by John Ringo use this very effectively, you don't even have to hear the music, but two main characters often submerge themselves in music and the playlist/lyrics they mention or sing under their breath while going on about their business (of killing zombies) absolutely set the mood/scene.
Stephen King does this somewhat as well in his books (But does a better job with it in movies, Don't fear the Reaper in The Stand was absolutely perfect)
Feeling great/confident: You can show through dialogue. "Hey, how's it going?" "Great, couldn't be better," he said, with glowing eyes. "You look happy. What's up?" "My girlfriend said yes," he said. "Congratulations."
Or, you can show it through actions. Maybe he jumps, or pumps his fist and says "yes." Maybe he yells in excitement like fans at sporting events: He yelled, something out of the ordinary as he was quiet and shy. A few people noticed and gaped. Even though people were watching, it didn't matter to him. He was thrilled to leave for his next adventure.
Think of why he's confident/feeling great. For example: His face showed glee and his heart beat fast with excitement; this was the first time he was setting sail on his boat. It was no ordinary boat; it was the boat he built with his sweat and tears.
Advice: make sh** up
One thing that goes with the feelings you're seeking is optimism. You can demonstrate optimism and confidence by letting the sailor deftly handle some ordinary snags on the way out. Later, you may want to contrast this with little snags becoming big deals, each one dragging Captain Gloomy deeper into funk.
