Think it through before you need to do it. Just the application of common sense really.
Take your aircraft (type), a good dog and handler and talk it through. Try it with everything stopped. I assume you will do "normal" pax brief things for the handler.
I have worked mostly with high skid EC135 with cabin floor pretty high off the ground. Found it best to get the dog lifted in by the handler via the rear clamshell door. Observer supervising and closes/locks clamshell door.
Handler on rear pax seat. Dog on floor with short lead between dog/handler. That way, the dog cannot get to the pilot
On exit use side door. Most UK police EC135s have high skids and significant drop to the ground. Handler will need a lead that is long enough to let dog out onto ground without losing control or strangling dog.
In the UK police ops are managed according to the Police Air Ops Manual. It is a CAA publication: CAP 612. There is half a page on police dog ops in there. Available from the UK CAA website:
The UK Civil Aviation Authority
They say dogs are most comfortable if they cannot see the view.......
Best to let dog/handler do it first in training mode, if possible.
If dog is unknown, a good idea to have a muzzle.
With Twin Squirrel/Twin Star there is less space. We used to remove the front seat observer, let dog and handler get in on the LH side. Handler on LH rear seat. Secure the dog on short lead. Front seat observer rejoins and closes door. Exit would be the reverse of entry. [Dog not far from pilot collective hand/arm on this one]