-When two Sims are completely in love, save the game before marrying. If the Sim says no and gives you a reason, go back to the neighborhood screen without saving. Go back to the house, and fulfill the need. If you ask the Sim to marry you many times over a period of a few days and then answer is always, "Can't you tell I'm in a terrible mood? Your timing stinks.", then give up. They are not meant for you.
-Invite the Sim over. Before she or he arrives, make dinner and get a radio. When the Sim gets there, greet them then start about three or four conversations. After that, the Sim should eat on their own. If necessary, move the food closer to the Sim. After they eat, start dancing with them one to three times. Afterwards, ask them to marry you and they should take the ring. If not, try again. If it still does not work, that Sim was not meant for you.