Belly fat is always LAST to go. Therefore, if you need to lose 10-20 pounds, for most people, it's in the belly!!! But that doesn't mean you need to TARGET your belly. I'm always yo-yoing 10 pounds on my belly. I've lost it countless times...and it creeps back...and I beat it back down:
Target your biggest muscle groups for most calorie burn : GLUTES!!! SQUATS!!! Pushups, lots of leg stuff....the big calorie burn and muscle work triggers allover fat loss. Core work too certainly to firm up that core and define the muscles that are UNDER the belly. But core work alone is not enough.
Clean, fresh diet. "Fit For Life" by Diamond (amazon) from 80's rapidly drops weight and makes it easy to maintain slimness with healthy eating. I lost 20 pounds on it in one month 4 years ago and then stayed effortlessly thin doing it for 3 years. Then I fell off the wagon, put weight back on this winter...and lost it AGAIN with exercise and Fit For Life eating. I'm 45.
My favorite exercise is always changing, but you basically need muscle work (weights, any of Chalene's Beachbody DVDs, Piyo, Turbo Fire, gym classes) and ALSO cardio like long fast walks, Zumba, spin classes. Both are needed. Muscle work AND cardio. For me, doing only either or never works. The last weight you'll lose is always the belly. So don't give up. It will go away.
Sleep. Water. Get the book Fit For Life. You'll lose 20 pounds in NO TIME eating healthy food in right combos at right times without calorie restriction.
Also, google your weight loss calorie count for your BMI and count calories for a few days with food journal. I know it's a healthy lifestyle no no, and I USUALLY don't count calories, but SOMETIMES when I REALLY need to buckle down, it helps A LOT to realize it's not that it's so HARD to lose weight, it's just that I'm EATING MORE THAN I THOUGHT...
I do 30-40 minutes of muscle work ( Chalene DVDs, gym classes-maybe your wii if it's strenuous enough) 3-4 times per week (to lose weight, less to maintain) and ALSO nightly long walks 3-4 times a week. Like a strength workout in morning, and some cardio at night. Spreading all workouts out over 4-6 days per week...less once I've lost the weight.