Set up your love scene realistically. Make sure it is true to the tone of your story. Don't throw in a love scene because you feel you have to, but make sure you work it smoothly into the plot of your story. Build up to the love scene the same way you would build the plot of an action thriller. Make sure it happens when it makes sense to the story's plot.
Create a romantic mood or setting. Determine what will work best for the type of story you're writing. For instance, if it is a historical romance novel that takes place on a 19th century French farm, then set the scene in places that will be familiar to the world you've created: a haybarn or a cottage or woods.
Be inventive. Find different ways of expressing the sexual and sensual details of your love scenes. For instance, gardening can be used as a way to introduce a love scene if one of the characters is a gardener. The character might show her lover how to sow seeds, holding his hand while they dig into the soil. The physicality of the soil and the closeness of both lovers can create an intense sexual experience that is consistent with the characters and the world they live in. If your characters have a particular interest (cooking, bike riding, skydiving), then find a way to incorporate those interests into the love scene.
Focus on the details. Use descriptions that will bring the scene to life. You don't have to pile on the details, but choose ones that will heighten the sexual tension. For instance, describe what the characters are doing or how they are responding to one another, either through dialogue or physical actions---"She felt his breath on her neck as she plunged her fingers into the dark loam."
Use the five senses. Let your readers see, feel, hear, taste, and touch what is happening in the scene. This helps build the sensual details that will make your love scenes romantic.
Use an "objective correlative." Poet T.S. Eliot describes an "objective correlative" as "a set of objects, a stimulation, a chain of events which shall be the formula of that particular emotion, such that when the external facts, which must terminate in sensory experience, are given, the emotion is evoked." In other words, it is a way to make the abstract (emotions) more concrete. When your character is experiencing love or sexual gratification, write it in such a way that you show rather than tell how she is responding: "When his lips pressed hard against hers, the blood rushed in her veins; she felt dizzy and she began to sway in his arms."