A good connection starts with the right tools for the job, some samples lugs connected for the kids to compare( lug fixture), and a testing procedure for the kids to follow.
- Wire strippers sized accordingly
- Wire cutters
- The correct crimper for the lug
- The right gauge wire selected for the job (Zip wire) ( standard servo wire with the right pins and hoods)
- Heat gun
- heat shrink tube
- holding vise
- Magnifier lens
- conductivity testing tools( multi tester or cable tester)
- The right solider gun for the wire being used
- flux
Try to standardize your lugs and cables. Try to use the same lugs for motor controllers. Motors that you may use over and over or need to replace quickly it would be good to use a XT-60 or Dean's type connectors which allows you to unplug the motor quickly.
Use good pliable wire for the motors at the correct gauge for the draw.
Lastly the idea of cable strain relief is important. Making a solid connection is wasted if the cable doesn't have the proper strain relief.