Top ranking for some keywords, not ranked for main.. ?

[tilbryllupet]

Hi again, I'm the owner of a Norwegian web shop, selling wedding favors. Now, the keywords I use is Norwegian, I'll try to explain:
I'm ranked 1st on google for "bryllupet" (the wedding) "bryllup stearinlys" (wedding candles) and lots more.. I've read about SEO a LOT the last 6-7 months, and I believe my page is highly optimized for this main keyword "bryllup" - But when a googler types in this word, she won't find my page, because some days the page are listed on page 57, other days on page 66.. 45.. 72.. and so on.. Some days I'm not even listed at all. Page rank is 1/10 and the page has been up since October. I know I need to update my page regularly with fresh content like articles or whatever, but this is hard since the page is an online store.

What should I do to get a better ranking for my main keyword "bryllup" ?

(I have about 2,7 million competitors, and about 500 incoming links - only 2 are showing up in link:www.mypage.com on google)

Any suggestions?