Instructions
Place Riolu at the front of your party and walk around the map. Just the act of having a Pokemon in your party and walking around will slowly increase its happiness.
Battle with Riolu as much as possible, but be careful not to let it get knocked out in battle. Using Riolu in battle allows it to gain experience, which increases its happiness level. Each time it is knocked out, the happiness level decreases. Whenever it gains a level, its happiness will also go up.
Purchase items to give your Riolu to make it happy. Giving Riolu a hold item will increase its happiness. Feeding Riolu food that it enjoys will also make it happy.
Treat Riolu to a massage at a Pokemon massage parlor. This will greatly boost Riolu's happiness.
Increase Riolu's happiness points to 220 during the daytime to evolve it to Lucario. Daytime is defined as the time between 5:00 AM and 7:00 PM in "Pokemon SoulSilver."