Start as you mean to go on.
If you think the puppy is nice to cuddle on the sofa, think about it when the Great Dane is fully grown. I’ve used the extreme example here but it’s the same for a Great Dane as it it is for a Cocker.
Be firm but fair.
Never let it in the bedroom.
When driving, either footwell or boot(with parcel shelf removed), never seats.
Plenty of chew toys if you plan on leaving it alone for a couple of hours. The elder of my two will rip a cuddly toy apart in minutes and the younger one will take his to bed and cuddle it. Two completely opposite dogs but inseparable. Both know the difference between their toys and the kids toys.
I have two springers (2.5 & 11.5 year old) that play by the rules and are pretty obedient, barring a few scatty moments and I think I’ve done a pretty good job.