First of all, no one just naturally gets good tech skill, you gotta practice it. Here's how I practiced my tech skill (I have a pretty fast peach with good FCs)
First I started by practicing FC Nairs without fastfalling. I would just FC and then Nair as soon as I felt I could. Once I got it to the point where I felt I could Nair immediately as the FC began, and I wasn't messing this up, I started doing the same thing, but out of shield. Once I felt confident in doing it out of shield and on the ground, I added in the fast fall and immediately did a jab jab as if I were attacking someone's shield. Then when I felt I learned the timing of the fastfall, I would just do FC Nair fastfall repeat as fast as I could. Once I did that, I would practice moving forward while nairing. Then I set lvl 1 bowser to heavy (handicap 9 vs 1, with a .5 level of gravity) and practiced it on the computer.
I personally felt that the FC nair was the only thing I needed to practice, and the others came easier once I had that down. I would say I practice about a half hour a day, but I do it just cuz I enjoy practicing tech skill.
I hope this helped someone...