BS: Might find that the Ab wheel is one of the better exercises for the total ab wall (lower & upper), including the obliques. Keeping the reps around 10 to 15, for 2 or 3 sets. The ab's should be treated like any other muscle group and really don't require marathon workout sessions. If new to this exercise, you will see right away the effect it has on the waist. Can use it at home, in the morning, afternoon or any time. Best to begin on a smooth floor, rather than a rug or whatever.
Vacuums are excellent, while holding the abs all the way in for a good 10 seconds, for each rep. Best done while at a 45 to 90 degree angle, standing and bending forward, usually with the hands on the legs/knees.. This is a Yoga practice and gives good results. Also helps when learning to breath from the stomach area, rather that the chest.
Pushing away is good. Watching the carbs is another option. The newer thing (at least in SoCal) is avoiding wheat/glutton products. A few women I know are doing the no glutton thing and it works very well for them. Carb reduction pretty much standard for removing inches from the waist area. With any of these, you need never to feel hunger. Smart planning is the key.
Male BB'ers, to give the illusion of a smaller waist, will work the outer/side head of the delts. Giving width to the shoulders (Larry Scott being the prime example). If having a natural wide waist, lateral raises, side presses, cable work,etc may help. Worth a shot. Good Luck.