Before beginning to overtake another vehicle, you should

• A. Sound your horn, move out and overtake.
• B. Check to see it is safe, change gear if necessary, and signal your intention before moving out.
  Explanation:

  "An overtaking manoeuvre requires that you do several things: check it's safe to go, change gear if you are in a manual vehicle and will need the extra acceleration, and signal your intention for enough time. Be sure to check over your shoulder before you pull out to overtake in case a vehicle behind you has already started to overtake you."
• C. Signal and slow down so you will have more room to overtake.