There are a number of ways to work out when to get ready for when the traffic light changes to green, for you to go.
The first is, while stopped at the red traffic light is to watch the reflection of the green traffic light for the cross traffic, and when it changes to amber/yellow and then to red, you can then expect that you will either get a green arrow or green light.
The typical cycle of traffic lights is that the right turn arrow operates first, followed by the green light to go straight ahead. So if you are approaching the traffic lights and the right green arrow is on, then you can expect that the next sequence of lights is a green light for you to go straight ahead. As mentioned, this is the cycle for the majority of traffic lights but not always the case, so approach at a speed you can stop.
Another indicator is when the pedestrians red flashing person stops flashing for the cross traffic, that’s when the lights are about to change red for the cross traffic and then followed by the right green arrow or green light for you to go straight ahead.