First of all check that your carry-on baggage meets your airlines specifications and that it is not over-packed and that it does not contain any prohibited items.
Limit the amount of metal on your person e.g. no big jewellery, belt buckles, watches, hidden body piercings. All of these items will sound the metal detector and slow you down.
Put any liquids, aerosols and gels into a resealable transparent plastic bag and place this bag in the tray provided at the scanner.
Do not carry any drinks through to the departure lounge.
Ensure that any electrical items like laptops and cell phones are places in the trays provided and passed through the scanner.
Have the items at hand before you reach the scanner. Remove your coat or jacket and belt before reaching the front of the scanner line.
Have your boarding pass ready to hand to the officer. Never joke about bombs or weapons whilst going through security. All statements are taken seriously and could result in a conviction.