Waste a lot of paper
Seen those movies where Romeos try to write romantic letters/poems/songs to their lady love, and end up with a room full of crumpled paper before they arrive at their masterpiece? Perhaps, it is a secret formula. For every 30 sheets you waste, you add a line. Three stacks of papers later, you might have your song.
Walk along the shore
Most romantic/break-up songs involve people walking alone on the beach, looking lost to the world, no matter what the rest of the world thinks. Smile at the sun, draw circles in the sand, run into the waves, splash around giggling and…. start singing.
Don't think too much
The trick to writing sappy love songs is to not use your brains too much. Take a bit from here, there and everywhere. “The best part of me is always you, I wanna grow old with you, and I hope you want to do that too.” See? That wasn't too tough, was it?
If you want to be a true connoisseur of love songs, you must necessarily spend three hours a day locked up in your room, listening to Taylor Swift, Backstreet Boys, Westside, Enrique, Britney Spears and Ronan Keating. Let the Masters inspire you.
Fall in love
You can't really think sappy unless you're in a sappy relationship, right? If you're a guy, find a nagging girlfriend, and if you're a girl, find a clingy guy. As you learn the intricacies of sappy love, the lyrics will start to flow!