Romance follows the same basic plot structure as any other genre:
- We meet the protagonist.
- An "inciting incident" disrupts the protagonist's life (in romance: (s)he encounters "the right one").
- The protagonist now has a goal (a relationship with the right one).
- Obstacles keep the protanogist from his/her goal (for example, the right one loves another person; or the protagnost has first to become attractive [economicall, phyiscally, socially, or in another way]; the right one is actually the wrong one, and the protagonist has to understand that the wrong one is actually the right one; and so on).
- The protagnost (or the right one) finally overcome the obstacles and they kiss or have sex or marry or whatever serves as the summit of fulfillment in the subgenre (Young Adult, erotic romance, ...).
- They live happily ever after.
Romance deviates from other genres in that its readers usually expect a happy end, but dislike "insta-love". That is, the protagonist and the right one cannot just meet, fall in love, and be a couple, they must overcome obstacles first. Love is the goal.
The common clichés follow both from the genre-unspecific basic plot structure, romance reader expectations, and from how love works in the real world. Of course, in the real world, there are relationships that do not happen: protagonists that do not overcome the obstacles and do not find fulfillment with the "right one". But those stories are not the subject of romance, but of other genres of literature.
As in other genres, you can avoid common stereotypes by following the conventional structure but adding uncommon twists. A hundred years ago it was an uncommon twist if a female protagonist did not marry the wonderful man, but elope with his sister. (If the protagonist is male and the female right one elopes with his sister, so that he essentially fails his goal, it is not romance but socio-critical literature or whatever.)
But even if you give your readers a common story, you can narrate that story in a way that makes reading the same old story interesting (e.g. humor or an uncommon perspective, such as a love story told from the protagonist's dog). Sometimes a twist is created by crossing over into other genres (e.g. the right one is a vampire; this was new in YA before Twilight). Or, and this is my preferred method, you can intensify the realism. Romance is boring, if it is the same story again and again. But if it is different people, experiencing the same things in a unique and individual way, then reading about the same basic things becomes interesting again.
So, as in any other genre, to write a good romance, you must not emulate the books that you love (that is, not write the 267th Lord of the Rings clone), but bring yourself into your book.
Great writing is soul searching. It implies honesty towards yourself. You don't have to write autobiographica, but put yourself in the protagonist's place and imagine how you would feel. Or, if you are one of the rare writers you can understand other people, become that person and feel how love feels for him or her. Do not just use the words you know have to go with the story, but truly feel the fear, the excitement, the sadness, the joy that you felt or saw in others. Observe closely what happens in and with and around you when you experience what your protagonist experiences.
And then you will find the small, seemingly insignificant aspects of love stories, that most writers overlook, but that give a story flavour and richness.
When you write what everyone has read a hundred times before, write that story from your heart and soul, with your voice, as you see it. And do not be afraid that your story will be a cliché. Because love, of course, is always a cliché, and at the same time, if you allow yourself to open your heart to it, it is at the same time the most wonderful and the most frightening thing on this world. Write from the middle of this contradiction – and then allow your characters the happy end most of us have not found in their own lives, or only fleetingly, only to lose it again.
In the end, dare to write the cliché.