Another good trick is to hold down the button for a second, twice, and then take a long draw. That's similar to taking a primer puff or two. This helped my 510 start performing. Also, what liquid are you using? The prefilled carts I got with mine, junk. Once I put some decent liquid in there the clouds started rolling in.
Also, if you're looking for a 510, try vapables.com or happy vaper (though they're out of stock at the moment). With shipping and exchange, you won't pay that much more and these are both good, local companies to deal with. Fast shipping, no border or customs hassles.