How do I reset NE555 output to LOW when powered on?
Pull up the reset to VCC with a resistor, and place a capacitor between the reset and ground, as show in the schematics.

When you power on the 555, C1 will hold the /RESET line for a brief time. This will reset the flip-flop of the 555.

NOTE:
The reset input current on the TTL version of the 555 is very high (between 0.4 mA and 1.5 mA) so R must be rather small. 100 Ohm will ensure that the levels are within specifications.

Adjust the \$R_1 \cdot C_1\$ time constant so that the low-level pulse is longer than your power supply turn-on time.

EDIT: The diode allows quick discharging the capacitor in case there is a very quick turn off/on cycle (thanks @Brian Drummond).







simulate this circuit &ndash; Schematic created using CircuitLab