Guidelines on writing userland software for ST-DOS
Keep it lightweight.
Don't waste resources. Support 8088/8086 when possible.
Don't touch the internal structs of the kernel.
The kernel takes care of all memory allocations and filesystem stuff for you. Don't try to edit the kernel structs manually - that will only lead into problems and your program is not going to work properly with different DOS versions.
Don't use undocumented MS-DOS syscalls.
Good quality DOS software works on all DOS implementations.
Make your program portable when possible.
If you are using a high-level programming language like C, support also other operating systems like Linux and BSD. This also makes the program much easier to debug.
Release the source code.
The user has the right to know what their computer is doing.