Hand Pumping techniques?

I'm EBF'ing at the moment but I may have to start building a supply for bottle feeding here in the near future so I've been practising with the hand pump. So far, without any help or instruction, I've managed to get about 2 - 2.5 oz per pumping session. I have a 2 week old baby who nurses quite often and I have had no issues with supply (that I know of...seems like there's milk aplenty) but it seems like I can't really get that much milk when I try to pump it. I'm wondering if there are some techniques I can use to get more milk per pumping session. I've tried massaging my breast but it only helps for a second or so. I know my baby can drink more than 2 oz per feeding cause he chugged that down and wanted more. How much should I be getting out? TIA!