In those days it is essential that people find your website. Be sure to include all words that are barely related to your page's topic, even if they are not contained, so users can find your page. You might also include results from other search engines into your website, like links to shopping sites, if your visitor wants to buy something.
Even if your website is completely static, it needs JS. Ideally, it should not even show any content without JS - if possible, make it get caught in an infinite redirection loop. Include JS from as many different TLDs and SLDs as possible. Let scripts load other scripts on demand. If scripts from some domain are not allowed, let the page remain in an indefinite state. Use the newest version of JQuery, but be careful to still not be compatible with older browser versions, except IE6, which is - of course - mandatory. Add handlers for common key combinations like Ctrl-W and Ctrl-Tab, so the user does not accidentally navigate away from your page. Add widgets that appear and follow the user, so he cannot accidentally scroll away from your navigation bar. If you are hosting an image gallery, use JS to implement an automatic slideshow that reloads the page and displays a random image every few minutes, even though the URL explicitly points to a certain image.
Your users will understand that nothing is for free, so you may include advertisements from many different networks. As these networks are often pay-per-click, it is totally fine to move them in front of your content, with a close-button that will open an external popup window. Some people like to open websites in the background and keep them there for a while. Since your scripts are reloading the page automatically, this costs you traffic, and so it is legit to use advertisements that make sound - nothing is for free. Furthermore, the content of your page may be split into many small parts, so the reader has to do many klicks to read it, and even more ads can be shown.
Never host downloads directly. There are lots of services like rapidshare or dropbox that will do that for you. If you really need to host content yourself - or maybe you are a content hoster - try to provide special download management software that optimizes your download - nobody wants to do large downloads directly in the browser, since browsers tend to crash, and the resume-functionality is broken in vitally any of them. These applications should require the newest version of Windows, since it is the most widespread, and therefore the most secure, operating system, and it is included in most new computers you can buy, so it is accessible to everyone. Some people are unfair and are only interested in your content, and not watching your ads at all. Therefore, make sure to hide the actual download links, and put links to your advertisement partner's software - again, nothing is for free.
Make sure that hyperlinks out of your website always run through your own redirection service first, which gets its information through a Referrer-header, and cookies, and HTML5 offline storage. For lowering of network traffic, you should additionally use URL shoortening services (tinyurl, tinyarrows, etc). However, a link to another website must have a good reason. Under no circumstances should you give sources of anything you include. The internet is a collection of knowledge, not a library.
Add a navigation panel with the links you consider important to the top of your page, as well as several sidebars with widgets, all following the current focus, such that they are always shown. Even on a 24'' widescreen, your visitors will thank you to just see a small 600px stripe of content in the middle of their screens, because everyone knows that this is easier to read. On small screens, these elements might disturb the experience, so when you detect a mobile device, add a popup that gives a link to an app for your website. For your app, you can port the relevant parts of your website to PhoneGap or Apache Cordova. Don't forget to provide a pro version that is ad free.
Using text is a simple way of assuriung that common search engines will index your page correctly. If you do not do sophisticated SEO in your meta-tags, at least some parts of your website should consist of real text. On the other hand, an important property of modern websites is that they need to look exactly the same under all circumstances. Some nice text designs are not possible with standard CSS, so it is good practice to just put the designed text into an image. This is especially important when you are a restaurant and publish your menu, so you cannot search through it. Sometimes you want text to be at a certain position, or you want text to appear not only on your website, but also on some image board. Then it is also common practice to put this text into your image. Also, for scientific texts that contain mathematical formulae, use images. Be sure to use a font that is not recognized by OCR, otherwise others might just pirate your text.
Generally, if you want comics and funny images, just upload them to an image hoster like flickr or 9gag, and include them in your personal webpage. You don't even have to give explicit links to original funny videos, even if you found them on youtube: Just make a gif-file out of them, most image-hosters support gif-files. If the dialogue is important, add subtitles. Remember to remove copyright notices and signatures, and maybe add your own, so the user does not get confused. Alt-attributes for images are there for witty notes, make sure not to put too much information about the image itself into the alt-attribute. Don't use the title-attribute for that, as it is a fairly modern attribute and might confuse older browsers.
Unfortunately, the common image hosters mostly have a size limit, so sometimes, you just cannot upload the whole video as a gif. So in some cases, it is the easiest thing to just embed the original video from a video hoster. If the user does not allow embedding, use your webcam to film the video playing, or some screencasting software, and upload the video from it, and then embed this video.
Videos and music should start auto-playing right over, so the user does not have to do an additional click, and can enjoy your website right away.
If you have a news site, an educational or a governmental website, or you are just legally obleged to, you might be interested in making your website accessible to disabled people. These people have a hard time reading text on images, or navigating through complex menu structures. Thankfully, there is JS: You can implement your own screen reader and braille output, as well as your own subtitle renderer. For mentally disabled people, just add a phone number, so they can ask you questions if they do not understand something. For foreigners, add translation links to Google translate.
You should add a doctype declaration on top of your html files, so it is not rejected by software that needs real XHTML. If there are some minor mistakes in your file, that is no problem, because high-quality software can deal with this.
When it comes to the internet, we are all on uncharted waters. (Angela Merkel)