There's a footbridge just south of the station (you can see it in the background of
this picture.) Just head out of the station, cross the footbridge to the car park beside the railway bridge (can take photos, but it's the access for the station from the car park, so is busy(ish)). Then walk down past the car park and around the corner at Domino's. Walk along past the car entrance of the car park, and you'll reach the footbridge. Maybe 5 mins walk, not far at all. It's not particularly scenic - it's next to the car park and a whole lot of business units. But you'll see everything coming out/going into the station from/to the South (which is the majority of services).
Also see
here for another location. For this one, I think it means you need to get out of the station, go under the railway with the road and turn right next to the Youth Hostel. This is to the north of the station.
From here you should see all services (I don't think there are any services booked to reverse in Platform 1, so all terminating services from the south reverse in the CS, to the North of the station, and would travel past this spot.