Hey first time poster here. Noticed this thread and thought I'd help out.
Using your DAW of choice, I normally drag it in (Logic Pro 9 for me) and set the video to the start of your timeline.
Then playing the clip make note of where your cues are going to change and any points of interest you want to accent in the score. Once you've spotted, as mentioned in a previous post, make notes.
Do not spot everything, too many changes in the scene will sound awful to attempt to score. Don't try hit every hit marker. See where it will flow.
Now before you start writing anything go to
http://www.fransabsil.nl/htm/eventhit.htmThis is a great tool used by tons of composers wanting to sync a tempo to the picture.
Its as easy as entering your length and time stamps to determine the use of the markers in your picture.
Once you have a tempo start figuring out where your beats/percussion are going to land.
I normally play the video again with a click track in place and record myself humming/tapping along to the picture for extremely rough ideas.
For parts where you go from one tempo to another or even switching the scene on an upbeat change the time signature to one slightly different to coincide with the spot.
The rest is up to your creativity. Hope any if this helps. Looking forward to chatting lots more on here!
anything else just message me bud.