Instructions
Invite the Sim you want to have a crush on to your house daily. A daily relationship bar must reach at least 50 for a crush to develop.
Chat with the Sim after he has arrived at your Sim's home. If the other Sim responds to joking in a positive manner, keep telling jokes. If the Sim only responds to talking, keep chatting with the Sim. Any time a Sim shows displeasure with a type of conversation, avoid it until the relationship has progressed further.
Invite the Sim to meet you downtown. Spending time with the Sim downtown dancing, shopping and eating can help to grow your lifetime relationship.
Flirt with the Sim after the daily relationship bar reaches 70. Continue to flirt with the Sim until a heart appears above his head. When a heart appears, the Sim has a crush on your Sim.