There are many better written guides available online than the ones that were here so I have decided to distill all the important bits into the points below:
Bandwidth is not free, try 7zip
Offer 7zip archives as well as zip, they can be much smaller in size (around a third).
Smaller image files means less space and faster websites
Run any PNG image files through OptiPNG (or a similar optimizer). Consider using Google's WebP format if it is suitable.
Think about your dependencies
For example, does your program really need an SQL installation? Would a simple csv file do the job?
Better offline documentation
A PDF document is much better than an offline website, a PDF is usually much smaller and is easier to search.
Move from .Net Framework > Core
A specific point but for some C# projects, this may just be a simple recompile using the .Net Core compiler to get a faster more memory efficient program.
All simple steps but together can make software and the web better!
On the basis that more people should be using a memory safe language and that the D Programming Language is very good, I have brought these guides back!
D versions of programs that can be found here and some thoughts about the language (mostly positive!).
Avi2Cvc from C to D
Some notes about the process of converting the Avi2Cvc program to D.
Converting Iff2Bmp to D
I made Iff2bmp in Go, Rust, Pascal and C and finally D! The version on this site is the D version, here are some notes about it!
This a single PDF which contains and replaced many of the guides which were this site, it also has more details about the above points.