With SEO (search engine optimization) being a big consideration when designing a website. The designer has to make certain design sacrifices to accommodate SEO. As search engine optimization doesn’t always compliment web design. However, it’s all about striking a balance between the two. Some of these compromises are as follows.

Flash may be pretty and look cool but isn’t helpful in SEO. The content of Flash can’t be fully read by search engines so all the text in a Flash file won’t be read by the engines and this can cause problems because when a search engine spider enters the website it will see it as containing no text therefore not appearing relevant to any search queries. Search engines love text and the more you have on your website the better. Therefore, this is why Flash isn’t a good idea. However, if used sparingly Flash can be a good asset in your websites design as long as you also include plenty of relevant text.

Image Links
An image link may also not be the best choice for search engines, although it’s still a link and will be taken into consideration as a valid link by the engines; from an SEO standpoint, you would be far better using a text link with proper optimized anchor text for the relevant key-phrase. A way around this can be supplying both a cool graphic as an image link and somewhere on the page a text link pointing to the same location. JavaScript drop down menus suffers from the same problems and the same solution should be applied.

Text and Color
If you text color is similar to the color of the background color of the web page this can also cause problems as spammers used to use this technique to hide text. They would make the text the same color as the background so you couldn’t see it. However, the search engines would be able to and the spammer would stuff key-phrases in the page to falsely increase its relevancy. However, the search engines have wised up to this and have advanced techniques to combat this. Font size should also be of a good size don’t use small font sizes as this can also be considered as spamming.

Source: http://www.quora.com