Shifting gears is hard... That's why everybody buys automatics.
Practice, practice, practice. The Z is definitely not one of the easier cars to shift smoothly from 1-2 a lower speeds, but it's not that hard.
When driving slowly, shift out of 1st at 2,000 RPM.
When driving fast, shift at redline... Smooth as butter.
When driving moderately quickly, shift at 4,000 - 5,000 RPM.
When driving as fast as the slow-poke in front of you... Have a jerky shift.
At least, that's when it always happens to me.