As pretty much explained in the other topic.
I have 14mm currently, maybe going 16 soon.
First stretch was 1.6 to 4, which hurt a fair bit actually, first stretches are the worst, but then again are proportionally the biggest.
Then 4 to 5 cos I got a free taper from someone, didn't notice even putting it in.
Then to 6, again didn't hurt.
6 to 8 by putting tape around my tunnels to make them slightly bigger, went smoothly if I remember correctly.
8 to 10 was worse than 6 to 8, but I think its because I made the tape crappy.
10 to 12 I put in without stretching.
12 to 14 was totally painless also.
I'd leave it 6 weeks at least after piercing to stretch. Then after every stretch, 2 or 3 weeks if you're in a hurry shouldn't do you too much harm. I've generally found you can put in 1mm extra everytime without it actually feeling any different, no pain at all. Go to 3 or 4mm at first. Standard ear piercings are usually 1.2mm I think, but lip studs etc are 1.6, so I had those in when I first pierced.