Certain assumptions about how your partner likes to live may
require fine-tuning now that you're living together. Co-habitation
isn't a life sentence, but familiarity can breed contempt and
living together should never be the cue for taking one another for
Certain aspects of your lifestyle will necessarily change now that you're living together. Initially, at least, an amount of independence built into your living arrangements will help - you don't want to feel like you're living in one another's pockets.
If you're moving in to somewhere new together, it's relatively easy to establish an agreed modus operandi. If one of you is moving in to the other's home, a degree of compromise is inevitable.
Be considerate. It may feel slightly unnatural, but always say please and thank you. Share the chores and cook together. Agree on a division of labour, establish the ground rules and don't apportion blame if something goes wrong.
Ask your other half before inviting your friends back and don't throw impromptu gatherings. Co-habiting with the opposite sex is very different to university days and living with housemates.
Be business-minded and reliable with money and bills. Have a frank discussion early on as to how your finances will be managed and apportioned.
Respect privacy and never open each other's post. Allow each other to have some space and independence.
Lastly, it is very unwise to buy before living together; a test run is an essential check on the stability (or fragility) of the relationship.