How to improve the python efficiency?

i am using arcpy to process some raster data and output a raster.
but now, i meet some problems.
1. how to flush the memory of temporary data.
2. how can i set a temp path for the temporary data.
3. finanlly and biggest problem is when i output a raster, it taked a long time (e.g. output a 18MB data need more than 10 min)?