Once you've established in the opening the attraction and the reasons why they aren't going to pursue each other then you create scenes and situations where they have to touch. Josie felt the warm strength in his hand, an image of those strong blunt fingers on her stomach flashed through her mind. Her skin tingled and she pulled her hand hurriedly away. The First Kiss. Now this is probably what you've been waiting for.
Sexual tension involves the first stages in the mating dance.
When the hero and heroine kiss for the first time they are going to have confirmation of what they'd been expecting and the additional spark of something more or they are going to have something unexpected. They'd been expected the friendly kiss of lifelong friends and find instead a spark of desire. The Mechanics of the Kiss . The nuances of the kiss are what differentiates between a spicy romance and a sweet romance. It's a coffee table book and has all these artsy pictures in it of couples embracing.