Make sure the water isn't at boiling point or it will burn the tea - let the kettle boil then leave it for a minute or two. Sencha green tea tastes much better than normal green tea. The bitterness is actually all the good stuff (providing the tea leaves aren't burnt) Try xylitol as a sweetener - it's made from birch trees and is good for your teeth!
In Japan green tea is, with one exception, never sweetened. The one exception is a sugary concoction made from matcha, the finely-milled green tea used in the tea ceremony. This drink is only found in the hot summer months. However, matcha powder is nowadays often used as a flavoring in cakes, ice creams, and other desserts.