Well, what software are you using, first of all.
And second, probably the most basic and yet most relevant tip you can receive: DON'T RUSH. I've learned this the hard way, and trust me, it helps to take your time. This applies to more than just making music, too.
Another tip: Find a bunch of music similar to what you're looking to make, and listen for the things that make up the song; how the beat is constructed, where the subtle shifts are located, basic tonality, etc.
Tweak, tweak, TWEAK those synths! A basic synth can go from great to horrible (or vice versa) with just an adjustment or two. A good melody is key to a good song; however, if your synths don't match the mood of the melody, or are just flat and boring, it makes for a crappy song.
One more: Ambience is key (in most cases). If you have spaces between notes/beats without anything there, everything will sound abrupt and the song will lack a filling tonality.
Other than that, just let your creativity flow. If you need a DAW (Digital Audio Workstation), I suggest
audiotool.com to get you started quickly.
Cheers!