Warning: Many have thought they controlled the narcissist, only to find themselves on the flip side.
1.- Listen attentively to everything the narcissist says and agree with it all. Don't believe a word of it but let it slide as if everything is just fine, business as usual.
2.- Personally offer something absolutely unique to the narcissist which they cannot obtain anywhere else. Also be prepared to line up future sources of primary NS for your narcissist because you will not be IT for very long, if at all. If you take over the procuring function for the narcissist, they become that much more dependent on you which makes it a bit tougher for them to pull their haughty stuff - an inevitability, in any case.
3.- Be endlessly patient and go way out of your way to be accommodating, thus keeping the narcissistic supply flowing liberally, and keeping the peace (relatively speaking).
4.- Be endlessly giving. This one may not be attractive to you, but it is a take it or leave it proposition.
5.- Be absolutely emotionally and financially independent of the narcissist. Take what you need: the excitement and engulfment and refuse to get upset or hurt when the narcissist does or says something dumb, rude, or insensitive. Yelling back works really well but should be reserved for special occasions when you fear your narcissist may be on the verge of leaving you; the silent treatment is better as an ordinary response, but it must be carried out without any emotional content, more with the air of boredom and "I'll talk to you later, when I am good and ready, and when you are behaving in a more reasonable fashion".
6.- If your narcissist is cerebral and NOT interested in having much sex - then give yourself ample permission to have "hidden" sex with other people. Your cerebral narcissist will not be indifferent to infidelity so discretion and secrecy is of paramount importance.
7.- If your narcissist is somatic and you don't mind, join in on endlessly interesting group sex encounters but make sure that you choose properly for your narcissist. They are heedless and very undiscriminating in respect of sexual partners and that can get very problematic (STDs and blackmail come to mind).
8.- If you are a "fixer", then focus on fixing situations, preferably before they become "situations". Don't for one moment delude yourself that you can FIX the narcissist - it simply will not happen. Not because they are being stubborn - they just simply can't be fixed.
9.- If there is any fixing that can be done, it is to help your narcissist become aware of their condition, and this is VERY IMPORTANT, with no negative implications or accusations in the process at all. It is like living with a physically handicapped person and being able to discuss, calmly, unemotionally, what the limitations and benefits of the handicap are and how the two of you can work with these factors, rather than trying to change them.
10.- FINALLY, and most important of all: KNOW YOURSELF.
1.- Never disagree with the narcissist or contradict him
2.- Never offer him any intimacy
3.- Look awed by whatever attribute matters to him (for instance: by his professional achievements or by his good looks, or by his success with women and so on)
4.- Never remind him of life out there and if you do, connect it somehow to his sense of grandiosity
5.- Do not make any comment, which might directly or indirectly impinge on his self-image, omnipotence, judgment, omniscience, skills, capabilities, professional record, or even omnipresence. Bad sentences start with: "I think you overlooked ... made a mistake here ... you don't know ... do you know ... you were not here yesterday so ... you cannot ... you should ... (perceived as rude imposition, narcissists react very badly to restrictions placed on their freedom) ... I (never mention the fact that you are a separate, independent entity, narcissists regard others as extensions of their selves, their internalization processes were screwed up and they did not differentiate properly) ..." You get the gist of it.
(Co-authored with Alice Ratzlaff - More here: "The Inverted Narcissist")