A simple question. But the answer is differentiated.
Do you already have many customers or would you like to win customers with a website?
If you already have many customers, you can send your customers a newsletter so that your website gets visitors. Your customers can tell other potential customers about your offer and recommend them to you to attract more customers. In this case, so if you are able to generate visits yourself, you can discount a few SEO criteria.
If you do not have any customers and would like to win customers via your website, then one of the main criteria is the searchability of your website. You have to do extensive SEO (Search Engine Optimization). So we have the most important criterion for a good website: it has to comply with web standards so that search engines are “ready” to include your website in the index.
Imagine, you are blind. Search engines see your website as a blind person. Search engines can not recognize images. Accordingly, the text plays a very important role. A good website contains good text / content. This content must have a specific structure for the search engines. The text can be edited in a very attractive way. Images should be used when necessary.
The text of an Internet page must be relevant to your target group.
Today, a website is viewed through many different media: smartphone, tablet, desktop PC. So the website has to be readable and appealing on these media.
A website is not a print medium. It is not possible to align everything pixel-exactly. The reason for this is that every PC user or smartphone user has different device settings. Another requirement for a good interest is therefore that it is readable on many different output media.
You already realize that the simple question is not easy to answer.
The question can only be answered individually to the needs of the provider. The answer is different for each provider.
Please have also a look to article “important factors for search engine optimization“