Instructions
Wake up your sim at around 6 a.m. Make sure his energy meter is full. Send your sim to the bathroom to shower and use the toilet.
Call the sim you intend to marry and invite her over. Make sure it's at least 7 a.m. before you call.
Go to the refrigerator and prepare breakfast, but don't let your sim take a plate yet. Send him outside to wait for the other sim.
Greet the sim when she arrives, then go get a plate of food. The other sim will do the same.
Get up when your sim is finished eating and go turn on the television. Ask the other sim to join you. If your sim's bladder meter is full, take advantage of this time to use the bathroom, then return to the television. Stay there until the other sim gets up and goes to the bathroom.
Stay near the television until the other sim finishes in the bathroom. Call the other sim over when she emerges.
Give the other sim a gift, then a kiss. This will raise the sims' social meters.
Choose the propose option. Your sims' comfort, fun and social meters are now optimized, so you should get a positive response.