It's happened to all of us. Heck, I just got my first flash that survived portal judgement through the portal! Here's a few suggestions:
1. Be original. Search NG a bit for stuff that HASN'T been done, or if it has, make a better version of it.
2. Exceed Expectations. Be elaborate. Turn what could be a two hour project in to two days or even two weeks
3. Add sound! (I know there's no sound in my tutorial and thats what is hurting it) People love something to listen to along with the flash youve created.
4. Read tutorials, ask for help, do whatever it takes to help you get the flash done (but no theft of others flashes).
Try using those tips when you try making your next portal submission.