The first full zip is amazing! Heck, even the hundredth is! As I'm sure my thousandth will be also.
I'm sure there is probably one out there, very likely even one right here on this site. In my opinion, the biggest thing to pay attention to is the membrane. As long as it is papery-white, to light gray (wet-looking white), then the chick is most likely fine. If it looks brown, its either too dry inside, or the chick is not progressing. Check out the "Hands On Hatching Help" thread, lots of knowledgeable folks when it comes to assisting. And of course, there are lots here too!
Also, in your researching, please keep in mind that different breeds are more likely to need assistance than others, and some breeds almost never need any (and if they do, its a good bet that the outcome is not as pleasant) Not all assisting is created equal.
Best of luck with your hatch!