int reading;
#include<LiquidCrystal.h>
LiquidCrystal lcd(2,3,4,5,6,7);
void setup()
{
  lcd.begin(16,2);
}
void loop()
{
    int reading=analogRead(A0);
    lcd.setCursor(0,0);
    lcd.print("Air Quality");
    lcd.setCursor(0,1);
    lcd.print(reading);
    delay(500);
    lcd.clear();  
}

Explain: 
	 DB7- to Digital pin 7
					DB6- to pin no. 6
					DB5- to pin no. 5
					DB4- to pin no. 4
					E(Enable)- to pin no. 3
					R/W (read/write)- ground connection
					RS - pin no. 2
					V0 - ground with resistor 330 ohm
					VCC- power 5v
					Gnd- ground.
	 For Gas sensor- 3 power point 5v and two ground (one resistor 1 kilo ohm.) and one analog pin.

OUTPUT: