Do not overuse Flash: apart from increasing the load time of your website, excessive usage of Flash might also annoy the visitors. Use it only if you must offer features that are not supported by static pages.
Do not clutter your website with badges: first of all, badges of networks and communities make a site look very unprofessional. Even if we are talking about awards and recognition badges you should place them on the “About Us” page.
Do not use harsh colors: if the user is getting a headache after visiting your site for 10 consecutive minutes, you probably should pick a better color scheme. Design the color palette around your objectives (i.e. deliver a mood, let the user focus on the content, etc.).
You’ve overlooked your target audience.
It’s easy to overlook your target market when you’re rushing to get your website ready to go live. But before your website can be successful, you must first carefully research your target audience in the specific market you’re trying to reach. Use your research as a foundation for the Web design process.
If you’re looking to reach women in the 21 to 30 age range, consider youthful color schemes and imagery, and cater to mobile website compatibility. As for an older target market, focus on larger font sizes and simplifying the user experience to help with faster navigation. Many Web design questions are more easily answered through target audience research.
And no, targeting everyone isn’t an option. Attempting to please the masses might leave you pleasing no one. It’s best to figure out your most frequent users and focus on creating the best possible experience for them.
Your website lacks mobile compatibility.
Seventy-five percent of smartphone Internet users prefer a mobile-friendly site, but 96 percent say they’ve encountered sites that were not designed for mobile devices. Do your research to find out the percentage of your visitors currently using mobile devices to access your site. If you’ve got a high number, consider developing a separate mobile version of your website or an app. For a low number, just make sure your website is readable on smartphones, but avoid investing in a mobile version.