Psychology in Website Design/ Ad Campaigns?

Why do some websites/ads succeed, and others don't? That's the question I'm seeking an answer to.
What are some effective colors, placements of products, upsells, etc. That you have found helpful in your endeavor of eCommerce?

 

>> Why do some websites/ads succeed, and others don't? That's the question I'm seeking an answer to.
A proper answer might run into hundreds of pages as it is a complex subject.
To cut a long story short, I can tell you what would not work for a 'successful' ad/site here:

1. Do not use a kaleidoscope of colors in a page. Be restrictive in the use of colors. The right color combination should be pleasing to the eye. Color is another complex issue. Culture, religion, race, location, average ambient temperature and a lot of other things have a bearing on color.
2. Do not use too many fonts in the same page. Just because you have them, do NOT use them.
3. The choice of props/images should accentuate the product and not detract.
4. Do not ramble on the text part calling for action. Most successful ads/sites use short pithy catchy slogans.

 

I would look up physiological color meanings and integrate those into your website. Then add some cognitive biases to give customers the extra push to click on your ad. This will increase your conversions.