Design your UX so that any large assets can be requested at will by the user, and indicate the file size? That way it's the user's choice if they want to load that large video over their slow network, etc.
> Every time a similar question is posed on HN, someone says "If the assets aren't needed, don't serve them in the first place", but this is i) unrealistic, and ii) ignores the fact that while the typical HN user may like sparsely designed, text-orientated pages with few images, this is not at all true of users in different demographics.