This is just a general recommendation, not a set of rules. Any reduction in page size is still a great step in the right direction.
LBP developers may want some level of styling. I recommend that they avoid as much styling as possible; however, if it is a necessity, it should be abstracted (unecessary detail should be removed) in order to reduce weight of the styling. For example, making ids and classes one character long would create a small difference in the amount of data required to receive a page. Developers should also try to avoid anything that requires much client-side proccessing (Try to stick to HTML and CSS).
Another option for images
Instead of including images directly in the page a link to the image could be provided. This way users can decide whether they want to load the image or not. Also, it would be ideal if images were compressed before being added to the website.