I have a routine I do no matter what. I do my burnout, get to the beams, turn on the pre-staged light. If the other persons pre-staged light is lit, I bump in until I barely turn on the staged light. I bring the RPM's up to 5g's and launch on the last amber.
If I turn on the pre-staged light and the other car hasn't yet, I sit there until the other car turns on the pre-staged light. After that, it's the same routine.
If you're opponent is completey staged and you're not, you can take your time getting pre-staged. Once the pre-staged bulb is lit, you have 14 seconds to light the staged bulb or you can/will be DQ'd.