Hitting the ball from Low to High help to generate topspin. The best approach to learn topspin is to use a loop swing (c-swing) instead of straight back.
http://www.topspeedtennis.com/tennis-lag-and-snap-technique/
Tennis Lesson in East Coast/ Marine Parade ( Laguna Green, Laguna Park, Villa Marina, Eastern Lagoon, , Casafina, Mandarin Garden, Seaside Residence, Bedok residence, Bayshore, Costa Del Sol, Seaside residences, Silversea residences, Shore residences, Tanamera, The Cape, Kallang)