Personally, I either pull the dog forward into a proper sit -- snug the collar up under the jaw -- or I lure forward with a treat. No cookie until its the picture I want to see. As far as lazy downs, that doesn't bother me as much. When doing a down-stay, I'd prefer my dog to "take a hip" so she's comfortable and at less risk of popping up. With sit-stays, though, those sits need to be correct.
Lindsay & the Gravity Dogs
"Though she be but little, she is fierce." -- Shakespeare