Good and bad practices in the making of a web page

According to a study by Microsoft, the first ten seconds are critical to the decision to stay on a page or not. It is therefore necessary that the reader is held by the appearance of the page, its introduction: communicate your value proposition within 10 seconds.
Because they are often disappointed by what they have seen before. But when they remain 30 seconds on the page, there is a good chance that they read in its entirety. To pass the milestone of 10 and 30 seconds, a Web page must be designed in a certain way, not just for the design, but for all that it contains.

Here is what to do and what to avoid in the design of pages for users, but also for search engines.

What to do

Filenames
They contain the keywords characterizing the page, separated by a hyphen. The same applies to anchors within pages.
File size
It can be between 10K and 100KB. A page that is too short will not get backlinks but if it is too big, it will discourage the readers.
Page title
It must be a sentence and not a list of keywords, from 50 to 80 characters, describing the site and promotional terms may be used.
The body of the page
Customers do not read, they "scan" the page. They are reluctant to read long texts not divided by subtitles.
Use CSS to separate content (and hence highlight it) of the presentation.
Use the tag <strong> which is an indicator rather than semantic <b> which is an indicator of presentation.
Subtitles
They should summarize the section or question to which they reply, and contain the main keywords for the section.
Images
The alt attribute must contain a description of the image.
Internal links
Preferably with the full absolute URL assigned to href, but it is not essential. Each page must be linked to another page and should bind the main internal pages.
Internal links appear preferably in the context, therefore in the text and not at the end of the text unless they have a global relevance.
External links
It is best to place external links at the end of the text (so that visitors do not move to another site before to end reading the content) and put links to good and relevant content.

What to avoid

Frames.
May hinder the work of spiders. They are now cleared by all professional websites. It does not encourage the reading of a page from another page, and are to be reserved for sites for private use.
Filenames.
This should not be noise words (1345.html) nor too general names (baker.html) except in a subdirectory with a meaningful name. Not a concatenation of words (bakeryPastry.html), even with a capital, or even separated by an underscore (backery_pastry.html). But significant words separated by a hyphen instead.
Page title.
Avoid untitled pages. If you do not use the <title> tag in the head section, you can give a title tag <h1> in the body of the page. Each page should have a different title.
Body of the page.
Long unstructured texts are rarely read by visitors.
Subtitles.
Do not use titles in a single word or common words like "Coming in", "And now", etc..
Images.
A page containing only images will not be indexed by search engines without all the meta tags. The images will not be indexed or rarely without alt tag.
JavaScript.
Not to be user to links or adding content in the page. Useful for Ajax, forms, etc.
Internal and external links.
Do not put links to pages that have a different topic.
Needless to repeat an internal link in the text, a link is sufficient, even if the word in question is used several times.
The flash graphic format.
Avoid.