ma_hty:
Among the 10 pitfalls mentioned, there is one bordered me, i.e. Method #10. It says lighting up 10 LEDs will damage the board. What should I do if I really have to light up 10 LEDs with individual control?
The reason #10 can damage the Arduino IC is that in addition to the maximum current each I/O pin can supply, each bank of I/O pins also has a maximum current that is significantly lower than then the total would be if all the pins in that bank were supplying near their maximum current.
The way you avoid the problem with a normal UNO would be to have a separate power supply for the LEDs, and then have each LED control pin connected to a low-side transistor switch that will turn the power to a particular LED on or off based on the state of that pin.