Three main components of any quality abdominal routine; upper, lower and transverse abdominals. If you neglect rotational exercises, your hips and lower mid section won't tighten up. Also, I recommend strengthening your lower back as well. Leg lifts utilize the hip flexors as the primary movers, while stimulation of the lower abdominals require movement of the pelvis not just the fibula.
Might want to investigate some deep breathing techniques, like those employed in Qi Gong exercises. Diaphramatic breathing can drastically improve the shape of your torso, even while you're sleeping. Check it out.
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