Definitely see an identical show home. We were ok to do this as there was one on the same estate. But just to get a feeling for the space and layout rather than their high spec fittings.
Also
check what the house will look like externally. This sounds stupid, but what I had no idea about (and no-one told us when we bought off plan) is that although the interior of the house was identical to the show home and sales blurb, the exterior was not the same.
In fact there are four houses on (phase 2) of our estate which are internally identical, but look very different from the outside. One of those is ours. (Build in red brick, black door, white window frames) one is the show home (yellow brick) , one has green wooden fascias and grey door, grey frames, and the fourth has different windows completely. For some reason our garage is in yellow brick as well, so it doesn't match the house. It honestly never occurred to me that it would look different to the pictures/show home. I don't mind it now but I was not happy at the time.
Definitely look at the plan hard. Check for overlooking properties, and not just the size of the garden and the direction its facing, but also the slope. We knew ours wouldn't be flat but its really annoying me now. We only got a bit of patio, but turf was included.
Also they wouldn't add in a garage door (as in a pedestrian door) for our double garage. It seemed stupid when they hadn't even built the garage yet, but it wasn't an option, so we will have to get one cut in at some point.
I pondered over the add ons for a long time, and decided that I wanted some in built wardrobes. In the show home, they had lots of them, but I didn't think I needed them all and I'm glad I just chose one each for the kids rooms as they seem much bigger than the show home rooms.
The add on price to add a shower over the bath was outrageous. We paid it anyway but seriously ridiculous.
The add on price to add rails to our walk in wardrobe (they don't come as standard - its just a small room) was also outrageous. Rails!
Agree streetlight. We have one directly outside our bedroom window, however I knew this was going to be the case so I bought a blackout roller blind as well as blackout curtains.
Don't forget to ask about charges. Maintenance/service/whatever its called, its whacked on top.
Get hold of a plan (for your location) and keep hold of it. Barratt homes conveniently keep being unable to locate the plans (seriously!) and we had to fight to get our tree in the garden, which we knew was on the plan.