Not restricted to smart stuff, but a bit of a brain dump after going through a large extension project and learning from my ommissions afterward.
At least two runs of Cat6 to each room, in places where you will either make use of it - behind the smart TV’s etc, or if you dont, then to a blanking plate next to a socket etc as you never know what the future holds.
Cat6 to an exterior location for in cae you want it down the garden at a later date etc.
Alarm cable and further Cat6 to every room - you may not want a hard wired sensor in each room, but at least you have the opportunity - make sure they are in the corners you would position alarm sensors in for best effect. The Cat 6 for possible IP cameras for a CCTV system in future. If you arent puttin git in now, just make sure you know where the cables are in the ceiling, because then you know you can break through the plasterboard into the corner and grab it. when the time comes.
Feed all these cat6 to a location that you will either designate as a comms room, or somewhere else appropriate.
Feed all the alarm cables to the location where you will want your alarm main box, and dont forget the runs of cable for the access panels.
Find the best position for your smartthings hub in the house, and make sure you have both power and cat6 to that point. The best position for mine is right in the middle of an upstairs landing, I have power, but no network so has to use a homeplug setup.
More light fittings/curcuits than you need. You can always lose them in the ceiling if you dont want them in future, but putting them in at the build stage is a LOT cheaper than getting them in afterward.
Handy ones we went for in terms of lighting were:
light switches near both sides of the bed connected to floor lamp sockets, so we can put on dim/side lighting in the bedroom for if you need to get up in the night, and you can turn the lights off from the bed. You can also turn them off near the door as per usual.
Individual security flood lights around the home, but they can also be manually overidden by a set of switches in the bedroom and also the kitchen, so if we hear a noise at night outside we can flick the switch and turn on all the front or rear floodlights. Hand for future automation and linking to an alarm, burgalrs dont like light.
decent speaker cable to above all rooms upstairs, Im putting this in now after the event and its a royal pain in the backside. Dont fall for the guff about “quality speaker cable”, Im using 4 core 2.5mm flexible mains cable. Its made of copper - and an awful lot of speaker cable is copper clad aluminium, which wont be nice for your amp. Its also 2.5mm so resistance is minimal (though Ive got some very long distances to run), and its about a third or less of the cost of similar quality cable marketed as speaker cable.
Ceiling speakers for the bathroom - great for keeping kids happy for bathtime, if of course you have kids or are planning any.
Depending on the size of the house and building materials you may want to plan for wifi boosters either in the rooms, or above in the loft. Modern building materials including foil backed insulation and even foil backed plasterboard do not play well with wifi signals.
Deep back boxes (useful for fibaro modules)
Neutral to the light switches (again useful for fibaro dimmers etc)
There are probably a lot of other things Ive forgot to mention, if I think of any Ill pop some more down, if it helps anyone avoid some of the issues or “it would have been nice if we’d thought of that” moments, then I hope its ok.