When I started to animate (not so long ago), I would usuallly go ahead and open my software and come up with something, and it usually does not look like what I had expexted, so I decided to organize my self and go step by step, and I will share them wiht you.
Step 1: Plan your animation. Write down every aspect of your animation on a script. For exmple what the background will look like, the characters, every single punch and kick, and if there's any aspect you do not know how to create, example a difficult effect, look it up and learn how to do it before you begin.
Step 2: Start animating with only two things; the background and the solid masses (stickmen, weapons, objects). Do not add any effects at all. But keep in mind that you will add them later and make your animation fit.
Step 3: Review what you have done.
Step 4: Add the smaller effects. By smaller I mean the ones that take up a small interval of space or time in your animation. For example particle effects, symbol effects, etc.
Step 5: Add the larger effects, example fades, color inversion. TIP: TRY TO MAKE A NEW LAYER FOR EACH EFFECT.
Step 6: Review again.
Step 7: Study your animation and build a suitable soundtrack in a SEPERATE program, for example Windows Movie Maker, Audacity. (You can still do it in flash if you find it more suitable. Keep in mind when working on one layer, you have to make a new keyframe in the correct position to add a new sound).
Step 8: Make a final revision of your work.
Step 9: Export your work into a video. TIP: DO NOT DELETE THE PROJECT FILES.YOU MIGHT NEED THEM LATER.
Step 10: Upload your video to Stickpage or Youtube!
I hope you found these tips useful. Happy animating!
EDIT: PATIENCE is VERY important while animating.