Main area's to loose weight and noticeably are the rotational parts, the things that you have to drive or have to be driven.. you can easily loose half a pound just on inner tubes, and rim tape..
Other areas I would suggest are .... Seatpost , bottom braket,
bars,stem,brakes,pedals,cranks,inner tubes, tyres, grips,wheel skewers.. cassette..
You could loose some off the cable's too.. non stress loading bolts replace with ally, stressed ones Ti. non essential loading nylon.. replace any washers with nylon or thinner ones..
But bear in mind the lighter you go , the more fragile the components become, especially if there not quality ones..

and the lighter better quality components will cost lots..
Weigh is not everything, and sometimes the lighter the bike, it tends to skip and bounce all over, and not track right,
Rotational weight first.
Static weight second..
