How do I improve efficiency of a boost converter?
Your inductor probably have high serial resistence. You might want to take lower value with thicker wire. Increase frequency if needed (but not too high, switching losses increases).
Use ulta-low ESR caps, tantalum ones. Add some 0.1 + 22-66uF of ceramic cap in parralel. If frequency is high enough just leave ceramic.
Implement synchronious rectification to get rid of that 0.25 vDrop (and I am not sure it's really 0.25, should be higher)
Use proper MOSFET. Why take 100V part? 1.5Ohm Rds? This is not suitable for efficient DCDC. You want some 12-24V logic-level MOSFET with some 0.1 - 0.01 Rds.