How can i check whether a plastering is leveled or not? And before plastering also how we minimise the defect in plastering due to leveling?

How can i check whether a plastering is leveled or not? And before plastering also how we minimise the defect in plastering due to leveling?
 
very simple.buy a 6'long aluminium mellet (size 2"x3"). with both hands place tight on the plastered surface.if the seller shows gaps between mellet and surface plaster is not even
before starting plaster place level tikki on a brick wall then do the plaster.
for any assistance and guidelines for the above subject you can seek the help of plaster Masson at site