Avoid uncommon plug-ins.
Rationale: Not every browser supports every plug-in. Many users are not willing to download and install plug-ins before being able to use a website.
Avoid more than one animation per webpage. Animations should relate to the content of the webpage. Animations and video should not loop endlessly.
Rationale: Less is more. Multiple animations per page detract from the content. Endless animations and videos can be very annoying.
Line up the contents on forms.
Rationale: This makes forms look more professional.