In my humble opinion (winks at dsvitak) the most important thing is posting for yourself. If there is a story there-great, it will develop on its own--but if you try to force a story, then the reader will feel that and will not get interested.
Craig (cknok0723--and this is a paraphrase) once said that he wrote out the first 10-15 post of the Pale Hose Dynasty just be sure HE was interested in the way he wanted to take it. For my next dynasty, I pretty much have drafts of the first 15-20 post already written--and that is not starting for at least another 6 months. I thought I could tell a story in my current dynasty, but without the "pre-planning" it just wasn't there.
These are my personal "4 rules of dynasty"
1) Don't overreach your time/ablities with a huge league. Sometimes smaller is better
2) Find your style and stick with it. If you are straying from your style, you're probably straying from what you are trying to do with the dynasty
3) Post for yourself, its the only way the dynasty will do what you want it too.
4) Before posting ask, will I need to know this when I reread this
In the Top 75 Dynasty Thread (which Y0DA55 is doing a great job on) he links to this
post by Tiger Fan that also has good advice on dynasties.