Recrystallization or purified through column chromatography.

you can remove the excess of aldehyde by washing  your mixture with a solvent  dissolve only  an aldehyde ..you know each reaction product  possessing a certain polarity .

Tan and Alaa gives you better way to purify your schiff base but you can also use saturated solution of sodium bisulfite...to remove excess of aldehyde.

I had this problem but I was able to remove the aldehyde by vacuum distillation (1x10-2 mbar) as Jeroen suggested. Crystallization is an other option. In some cases the imine is not soluble in diethylether (obviously it depends on the imine you have) whereas the aldehyde is. If the case you can wash the solid imine with this solvent on a filter.

you can wash your mixture with EtOH, H2O and diethylether

Thanks colleagues

You must Know the best solvent for this aldehyde at room temperature usually it may be 50% Ethanol or Ether this depends on starting aldehyde material if your aldehyde has along non polar chain it may need  50% isopropanol solution to dissolve it also you must be sure that your product doesnot dissolve like your starting material in these solvents