Here's a workout that's sure to help your core strength. Make sure you focus on pinching your back while doing the facepulls, to keep the work out of your biceps. My ballet teacher would always say "keep your wings down and back" That's pretty much right on the money. Making every rep slow and deliberate also helps work the core, especially on those single arm dumbbell presses--you'll feel the pull while you struggle to keep everything in line.
Do these as circuits, so that 1a, 1b, and 1c are done consecutively without rest. Rest in between sets, but only from 30 seconds to 2 minutes MAX. For the 2a and 2b, do not rest at all. Use this a a burst of cardio for some extra fat burning, and make sure your weight is light enough that you can do at 5 reps on at least the first 4 sets.