Just keep up getting more links regularly and update your content from time to time Check out what the competitors are doing! That should prevent you from bad surprises.
Be the best site for the targeted keywords. If you're not #1 you won't stay without hard work. If you're the best, people will naturally link to you and keep you in your spot with minimal work.
It's hard work and not an exact science (at least from my experience). I've gone from #1 to the world beyond the #200 results for a search term with my SEO practices. To many of the same keyword links which put me at #1 but I guess eventually made the big G angry and kicked it out of the field. But for everything else I'm still doing fine. Knock on Wood...
nothing will soothe daddy G's soul and keep him happy with you more than natural links and new original content
Thats very true and it's important not to forget to remind people to bookmark your website. Sometimes bookmark web pages end up getting well endowed with PR or popularity. Even better is that those bookmark links will probably help with personalized search in the future as SE's keep track of what you and other people browse, tag or save in your bookmarks.
My simple suggestion would be to keep doing what you did to get there in the first place without overdoing it ofcourse.