I hate when this happens! What i like to do is make a list of some things going on in your life. Maybe you have a best friend going through a tough time, your wife just gave birth, or something. Even the little things count like someone did something really nice for you etc. This helps give inspiration as to what you might want to right about. Another thing i like to do is look at some songs from other artists to get inspiration as well. In the end you might not be using the same topic as that person but it helps get your mind flowing. If all else fails take some time off and let the ideas come to you because that's a lot better than trying to force ideas out. Sorry this was so long! Good luck :)
I would tell you some but I'm working on them myself and don't want to give away my ideas. Not to be mean or anything, just that I've been where you are and when you finally have an idea and it gets stolen it really gets on your nerves.
For a song to be successful (besides the talent of the writer) it has to inspire emotion in listeners. So it needs to be inspired BY the emotions of the writer. What are you feeling? Are you angry about something? Write an angry song about it. Are you happy about something? Write a happy song about it. Are you in love? Write a song about how that feels. Look at your own emotions and draw inspiration from that. Songs written based on someone else's "stated" emotions tend to fall flat.