Depending on the circuit you are using it in, you should be able to get reasonable efficiency from this IC. All of the components will affect the efficiency, not just the chip. Are you using the internal switching transistor or an external one?
I find a good way to optimise for efficiency (once you get into a power class over a few watts) is to find which components are heating up. Then ask yourself why they are heating up and how can you stop them from doing so. If the inductor is getting warm, can you use one with a lower DC resistance? Or is it saturating? Losses in the switching transistor could result from Vce_sat/Rds_on being too high - could you use a part with better specifications? If the losses are from switching, rather than static, can you provide a better drive signal? Or perhaps redesign to use a lower switching frequency?