How often do you update your creatives and what converts best

I've noticed quite a few threads here focus on getting traffic but I think despite having a good website with content if the call to action isn't placed correctly or if the creatives to content ratio isn't right there is a good chance that conversions won't happen.

This is more important especially when promoting merchants through an affiliate program.

I'd like to know/learn from other's experiences in this regards.

1. How often do you change/update the creatives:
2. What converts best, banners or text links
3. How many links (affiliate links) should an article with an average of 500 words have