CONTENT: Your content has to be well thought and free of any spelling or grammatical mistakes. Make sure your language is adapted to your target audience and always be honest about whatever you do. Don't make promises you can't keep!
DESIGN: The design of your website is fundamental! Pick a clear and simple design that makes you look serious and that fits your content. Try to use no more than 2 or 3 different fonts. Good quality pictures and a logo are also a guarantee of quality for the visitor.
DOMAIN NAME: Having your own domain name is a definite asset. It's perceived as a sign of credibility for most of the web users. It's an effective and inexpensive, and is an inevitable part of the process to gain your visitor's trust.
KEEP YOUR SITE UPDATED. It's the best way to show that your company or your organisation or whatever the reason you do a site for is dynamic and flourishing. A site that has not been updated for years is generally a bit shady. We recommend you to use your homepage for these updates so people see it first.
REALITY CHECK: Display your physical address and your and opening and closing hours. Feel free to highlight the different ways to contact you ( email , phone , chat ...). People trust more easily an organisation that shows proof of its existence in real life. Put the history and the experience of your organisation forward. Introduce the people who work there so the visitors know he deals with other human beings. If you wish to stay professional on your website, social media is the perfect place to show the human part of your organisation.
VISIBILITY: Increase your visibility on the web through social networking, advertising campaign or good ranking on search engine. People will be more likely to trust a site that exists elsewhere on the web. And it's even better if you have followers, fans, clients or contacts with other oganisations who certify that you are reliable.
Most of this advice should be instinctive. When you create your website, just think about what it takes to make yourself trust a website when you are on the web. And if you don't trust your gut, make a checklist (with this post for example) and be careful you meet the criteria!