Assuming you mean you can't really get an idea going, I guess I cant sorta help. I myself am fairly new to making music with any program on the computer(been working with FL for a couple months only) and I have always had trouble creating a good song too, and that also applied to the instrument I have played. One problem I ALWAYS had was that I would get something that sounded really nice up, but then I could NOT progress any further with anything matching no matter how hard I tried, and well, I give up easily.
SO, what I like to do is start off with a drumloop, whether it is a preset one, or one of my own, I just need something that sounds nice, HOWEVER, when you start FL studio up, the default kick, clap, snare, and hat aren't usually something you would want to use when making your own. I personally prefer using CB_Kick, CB_snare, CB_hat, CB_clap for my drums, but if you search around in the preset drum sounds, there are MANY many more you can choose. For synths, it honestly depends on what I am making. I like to use Sylenth 1, NI massive, and Sytrus for my synths, and while NI massive is honestly the best out of those all, sylenth 1 and sytrus come in use sometimes also. Which brings up the next thing, once you get your drums figured out, you can slowly work your way up with synths, adding them to the song, seeing how well they fit with the drum, editing them, adding them, deleting, re-doing, etc. But only work in small sections until you get a really nice sound, otherwise it might end up being ruined.
Oh, and white noise sweeps, probably my favorite thing to do in FL studio, here's how it's done.
http://www.youtube.com/watch?v=ZHFRUCMlgj4This guy also has some really useful tutorials for FL studio, so definitely check out some of his videos.
Ok, that's all I can think of as of right now, hope it helps c: