I can't give anyone a complete rundown on how to write a romance, whether it's contemporary or genre based. But here's some blunders I hit along the way with my first attempt at this type of book.

Read the romance category or genre--at least a dozen books or more to get a feel for what's been done and what's being written now. It will give you an idea of how to write a character-driven story, rather than a plot-driven book, if you haven't gone the character route. There is a world of difference, except in sub-genres where the plot might be more crucial to drive the story along. It's all about the people, first and foremost folks.

Intimacy is important, including dialogue and inner monologue. This is a love story between any individual types. Let the romance flow, make it touching, meaningful and intense. The characters must be attracted to each, more so as the story unfolds, but not necessarily in the beginning. Inner thoughts and emotional feelings are very important.

Sex scenes, or passionate love-making scenes are not a laundry list of sexual gymnastics: stroking, sucking, fondling, blowing, sticking, juicing, whacking, plunging, licking all those naughty terms, unless you need those graphic examples for a certain emphasis. Use some metaphor to describe emotions and physical contact unless you are seeking a certain heat level where it can demand more explicit descriptions, including erotica. Is it a love tunnel, pussy or vagina? Make up your mind and try and stay within such body part names and tags.

The pace is a little bit more leisurely in a romance, not quite the SF shoot 'em up and let off mass explosions that kill dozens of people, unless there is a very strong sub-genre holding the story up. Some epic (saga) and historical romances might explore the backdrop of a major war or conflict. So that can be perfectly acceptable.

Read the Publisher guidelines. What is the editor and reader fan base looking for? Do you need the female MC at center stage with a full POV? Does the male or other lover need a POV or not? Are male-centric romance stories okay without a female POV, or should there be a balance of some type? Typical Alpha male or not? Is "nerd" romance acceptable with this publisher? 

These examples were my major stumbling blocks. There are more for sure. Read up on formulaic or category romances and see what the differences are. For instance, the publisher might want an emphasis on men or women in uniform, country folks, doctors, cops, cowboys/girls and other specific types.

Are you writing Christian romance which has sweet and behind-the-door sex? Don't send erotica to a publisher who doesn't go for it. 

Happily ever after, unresolved or tragic endings also have a determining factor when selecting a publisher.

Harlequin (a category romance type) has very precise wants and needs, and you must follow those guidelines to break into any of their romance genres or other imprints. 

Live easy, love hard.

Chris