There are probably more website design mistakes to be avoided, but these are found by researchers to be the most common mistakes.
1) Publishing really, really long web pages the require users to scroll and scroll. Guess what, they will not do it without the content above the fold – that is the initial screen range – is super interesting. If you manage to engage them, and you've got to be good to do it, do not make them scroll, give them a link instead.
2) Opening new browser windows from your site. This is a mistake web designers are still making and it's easy to understand why. The theory is that you want to leave your site open and waiting so when the user wants to return, it's there for them. Wrong! Users do not like the control taken away from them – they believe they are all powerful and the back button works just fine because they know how to use it to jump several steps back.
3) Resizing the browser window to meet your display needs. This is just lazy a lazy technique (trap) that some website designers fall into to please their clients who want the page to look exactly this way. Plus, remember what we said in # 2? Users do not like the control taken away from them, so leave it in their hands. They are mature, they can handle it.
4) Playing music or overusing flash. In the early years, it was a fun trick for website designs to include music – it showed that your web designer knew that tag, but that's all it did together fail miserably. Apart from increasing your web design's load time, excessive use of flash is likely to annoy more than it is to charm your users – especially if it starts automatically. If you want to use flash, let the user choose to start it or not.
5) Using a home page to launch the 'real' website. The fewer steps it takes for a user to get to your real content, the better. This is something web designers simply have to grasp.
6) Breaking the back button. This is a basic principle of website design usability. Do not override the browser controls under any circumstance. Again, treat your users like they know what they are doing and let them keep the control.
7) Cluttering your website design with badges. First, lots of badges and network communities look like you're trying too hard. Even if you're talking about rewards and recognition badges, these should be placed in the content content instead as supporting material and less of bragging rights.
8) Blending advertising within the content. If your web design is using advertising like AdSense units inside your content, you'll likely see a brief jump in your click-through rate, especially if you have family and friends checking it. Over the long haul, however, you're far more likely to lose readership through sheer annoyance.
9) Using 'click here' instructions when you should use anchor text. This is a common mistake made by website designers all the time. It's easier to say click here than it is to craft good content that creates the anchor link, but anchor links and quality text increase your SEO across your website design.
10) Requiring registration to use your site just because your marketing team said to do it. Users are used to free stuff, and let's face it – they have loads of options. If what you're web design is offering is not really valuable they do not have to register for your site, they'll just find it somewhere else. And one other thing – never subscribes the user without their consent, do not subscribe them to your newsletters just because they registered, and never send them unsolicited e-mail messages. This is not a way to make friends; it's a sure way to make enemies.