Design logical structures. It is best if the DOM (Document Object Model) matches the visible order of elements. Design your elements the way people expect them to work, don't use common elements in a different way than they are usually used. This will only confuse your users.
Always design controls for content that starts automatically, for example, carousels. But avoid the content starting automatically. It is always better for the user and accessibility if they can control the content. It will also be better for green code principles if the developer can load content only after the user wants to play it.
Use headings and spacing to group related content. It helps make the content easier to read and browse.
When designing the layout, remember not to have too long lines. Generally, it is considered that a line shouldn't be much longer than 66 characters. Longer than that and you will have to start turning your head to be able to read the text.
Remember to think about screen magnification users when designing dialog boxes. If the dialog box appears out of sight for a user, it will be very confusing and usually, the user cannot access the content.
When designing language menus, avoid using only country or language codes. Not all people know what they are. Better link texts are "In English" "På svenska" etc. If you want, you can include also the codes, but I recommend having those only as an extra set of information.
Avoid using only flags because some countries have more than one official language.
The globe icon is often used for indicating the presence of a language menu. But there is a language icon you should use instead. Learn more about the language icon. There are also more stripped down versions of the icon that you can use. The globe icon is quite well known though, at least I've seen it on a lot of websites. If you have a country version, then the globe icon might make more sense. In either case, try to avoid having the icon as the only way to identify a language menu.
It is recommended that you always have a breadcrumb, especially on larger websites. Breadcrumbs help people know where they are on the site.
More about the language icon on languageicon.org.