Common Website Issues
Links to other pages don't work anymore
If you changed your website url and didn't use relative links, it'll still be linking to the old url.
Example
Absolute link: https://mysite.neocities.org/about.html
Relative link: /about.html
My images don't work anymore
Image hosting websites will delete your images at some point. It's more reliable to locally host your images (aka put them with your website files and link to them). If you're concerned about size you can compress your images to make them smaller.
My website isn't responsive
You need to make it responsive from the start. It's easier to redo your design than try and force it to be responsive. Use flex or grid depending on what you need (Flex is easier IMO)