Need tips on how to do a STANDING back tuck?

I can do a running roundoff tuck, and it's really high and everything..but I tried doing a standing tuck, not on a mat or anything, just at home on carpet, and I got it, but then I started doing something different with my head or something..and I fall on my knees..Like, I don't know what it is..I look back or something so I need tips on how to keep eyes? Like look straight or what?