Relationships, especially in beginner writer's works, have a tendency to feel forced. Even in some popular and famous works of fiction, the relationship doesn't feel natural. It seems like a boring afterthought which the writer added in at the last minute. Far too often, I find myself completely indifferent to a character's romantic life. A good romance in a story will give the reader a bit of second-hand infatuation. They'll root for the relationship, beg for it. If the romance is well written, you can make a reader smile and blush just by reading a few sentences.
When done properly, it can even compensate for a weak and cliché plot.
But first, decide whether the romance is needed. If you're adding a character to the plot simply for the sake of being a love interest, it's probably not a needed romance. You can still add it, of course, but it will be much harder to keep your story focused on the central plot.
Step One
Make sure the characters have chemistry.
The characters should complement each other's personalities. If he's loud, stubborn, and aggressively opinionated, a more tranquil and soft-spoken love interest would suit him well. Two headstrong people wouldn't be likely to have a lasting relationship in real life, unless the (impossibly) agreed upon every subject. But, there should be some similarities. While opposites do attract, polar opposites will not and the whole relationship will feel forced. The characters should have something in common. It could be morals, a parallel backstory, the same motivations, whatever. As long as there's a reason for them to be drawn to each other, there's potential.
Step Two
Slow burn ships are fantastic.
Don't make your characters fall in love right off the bat. There can be attraction, of course, but genuine feelings of true love don't happen instantly. Your characters should become closer as people, feel at ease around each other, and truly know the other before they can fall head-over-heels. The readers will crave the relationship far more, like dangling a treat right in front of a dog's nose, but keep pulling it away. Teasing is a beautiful thing.
Find ways of showing (NOT TELLING) the characters are falling for each other. Have them stand up for one another, be protective. Have them break their own normal routine for the other. For example, a callous, guarded character could lower their walls for a moment if their love interest needs emotional support. These scenes can be awkward for the character changing their typical behavior and that discomfort can demonstrate how much they care for the other, altering their own selves for the other's benefit.
However, make sure that you combine these cute emotional moments with distance. Make the characters deny their true feelings or even distance themselves from the love interest upon discovering their feelings. The more the characters long for each other, the more the reader will long for them to be together. Build barriers between them for your characters to have to work to knock down. Keep them close, but maintain that distance until the moment is right.
Step Three
"____" translates to "I love you"
The first example I think of when I think of this is The Princess Bride, where the male protagonist tells his soulmate "as you wish" when he really means "I love you".
This falls under the category of show, don't tell. Hearing a character say, "I love you" has become so boring. Unless it's done in a surprising confession or unique way, it's boring and stale.
Come up with a phrase that you can repeat in moments throughout the story until it has a meaning of love for the characters and both know exactly what the other means when it's spoken.
Step 4
Taking a break can help create tension.
You know you loved someone if you leave them and feel awful. Apply this into the writing. Your characters can break up, then get back together in a joyous reunion.
Step 5
Not every couple has a happy ending.
Sometimes, things don't always work out for different reasons. An ending that leaves readers craving more can be a good move.
