Here are some of these,
1. Good power supply : A reliable SMPS is a good choice over transformers.
2. Use of soldering flux : NEVER forget this.
3. Use of hot glue : This baby is really helpful to keep those fragile parts safe.
4. Use of spacer nuts : Use plastic/rubber spacer nuts if you use metal case.
5. Glass epoxy boards : Prefer over paper phenolic.
6. Ground plane : Fill empty spaces of copper layer with the ground plane.
7. Switches : A part prone to malfunction. Use good quality ones.
8. Pots and presets : Same here.
9. Tie all the cables : Make sure to separate power and signal cables.
10. Try to incorporate all the things in one package. Avoid interfacing too much parts.
Finally,
Your software Part.
1. Note all the exceptions that may happen and include a code to handle them.
2. Place some status LEDs. This helps to debug the problem.
3. Place an activity LED, like one on the PC.
4. If code is perfect, prefer OTP chips over flash ones.
Hope this helps.
Good Days