Hello all, long time lurker, first time poster, please go easy on me if I accidently say something stupid, I swear I didn't mean it

I've been using article marketing (mostly Ezine Articles) for about a month and while I've had only a few successes (my fault for being less than diligent with it) I will keep learning and improving on my mistakes until I figure it out. That said, I have a few questions about article marketing and how to best go about using it:

It seems that an articles ranking will drop after a period of time, how can I get them to STAY at the top, particularly if a specific article converts well?

If I have such an article and it's impossible and/or it's too difficult to keep that article ranking well, is it a good idea to, say, create a new account and write an entirely new, but thematically similar article that's optimized for the same keyword as the original that has dropped in ranking? I say create a new account because I don't think Ezine Articles like having very similar articles in the one account.

Are writing original, quality articles and submitting them all to Ezines an effective way to help with SEO? How does it compare to directory submissions or forum sigs?

Thanks for any and all help.