I drink green tea 90% of the time and have for years. But even more so this year since I eliminated black tea from my menu. Jo, if you are not getting more than one infusion, it may have nothing to do with how you are preparing your tea.
I have found that Japanese tea of a broad price range from a very reliable source will give 3-4 infusions....the first is light and fragrant , the 2nd is the best and the boldest and usually the greenest, the 3 &4th I start increasing temp and reducing water used...the results will vary greatly depending on the tea. But for Gyokuru, you should be able to get at least 3 infusions and often 5 assuming the tea is not old or stale and has been preserved properly. It is important that once you open a Japanese green to use it within 1-2 months...that is critical. Always make sure you are buying current harvest Japanese tea, and if it has been nitro flushed in Japan that is the best...Japanese tea detiorates very quickly when it is exposed to air, light, etc.
Chinese greens are so variable in leaf form and manufacture...it is impossible to give a rule of thumb. Long Jings, my fav, should give 2-3 quality infusions...again the tea needs to be fresh and stored properly.
Generally, I get 2-3 infusions from my Chinese green tea...but I always buy fresh from a reliable source who is willing to share harvest info, especially season and year of production. I recently discontinued using a vendor who simply would not share this info...they have a bijillion teas...probably half of which were from the previous year. That will not cut it. As buyers of premium green teas, I would encourage you to insist that harvest info be readily available and prominantly displayed on your vendors site. If they refuse, it may be time to move on because there are many reputable vendors who readily provide this info.