Practice the song so you know it well. It takes time to warm up your vocals and get into the groove of the song. Don't sweat the punch in. The main thing with a punch in is that it sounds the same as the other vocals around it. So... if the punch is done the next day..... be sure you have warmed up to the point you were at when the surrounding tracking was done. I have even gone as far at times to record the entire vocal track again because the punch sounded different from the existing material.
Pitchy vocals come from not being warmed up, straining, singing without control, too loud, too quiet, and lots more things...... just aim to get them as close as possible. Melodyne can fix many bad vocals.
Tone quality..... see the line above^^^^^ focus on the quality of the vocal part.
Clipping... to close and loud for the mic..... weak vocals, too quiet of too far away from the mic.
Use mic technique. When you know a loud belt it out part is coming.... back away and even turn off axis to the mic by 45 degrees or so. If it's a quiet part, get up close. Use a pop filter.
I often sing with no pop filter close up with the mic beside my mouth and I sing 45 degrees past it so the plosives and sibilant sounds don't get jammed into the windscreen.
If you want to sing... it's just like playing an instrument. You have to warm up, and practice every day to get good at it and develop the control and tonal qualities you are seeking.
I sometimes will lay a track in one take. Fix the bumpy parts with melodyne and let it roll.
Oh yeah... another good tip..... use a good condenser mic.