Laying low at home is great. Otherwise I love walking the Sydney Harbour Bridge with my partner from the city, and then we walk around and have dinner at one of the beautiful Thai or Italian restaurants at Kirra.
If I have a few drinks, Darling Harbour it is - or the Opera Bar at Circular Quay.
After a nice dinner at Darling Harbour, I like to go to King Pin bowling for a few games and a round or two of drinks. It's fun with a group or just two people, the music is good and there's always the option of laser tag afterwards, or hitting some nearby bars.
If your in the mood to get dolled up for a great Friday night out, Ivy Pool Club and Bar on George St is one of the best places to go. With a very sophisticated yet chilled and relaxed ambiance, its a great place when you want to shout TGIF off the top of your lungs. Although they are a bit pricy, their renown cocktails are fantastic (I recommend their Long Island Ice Tea if your taste buds yearn sour flavours).