Imam al Reza (as) : Do not engage in sexual intercourse unless you engage in foreplay, and play with her a lot and caress her breasts, and if you do this she will be overcome by passion (and excited to the full extent) and her water will collect. This is so that the emission of the watery juices shoots off from her breasts and passion becomes evident from her face and her eyes and that she desires for you in the same way, you desire for her.
Divine Treasure 