Suggest a few ways to build software to stop weakening due to change?

Answer 1

Make sure that software is designed so that changes in one part of a program do not create side-effects in another part of the program.
Make sure that software is designed so that it does not depend on external devices or systems that are likely to change with time.
Make sure test cases and results are archived and available so that the software can be retested when changes are made.
Make sure you spend time understanding what the customer wants.

Answer 2

1. plan and implement archival strategies for the file system and database
2. consider data partitioning for huge tables
3. review database indices to remove old and unused ones while creating new ones where necessary
4. review the hardware capacity and resize as appropriate
5. make use of multi-threading/ multi-processing where necessary (only if such skillset is available)

Answer 3

take more time in requirement gathering stage and also make your software such that its easily maintainable and can be updated easily.