I have big hands so this might not work for all of you but here's what I do, and I've racked a lot of balls!!!
I put the one ball on the spot, with the other balls loosely behind it and the top of the rack firmly against the one. Then I bring the rest of the balls up to the one with my right hand until they're snug against the one. Once all the balls are tight, I use my first, second and third fingers to gently spin the balls in the back and middle of the rack towards the one. This helps make all the balls cinch up tighter. I then push the rack gently forward until it's not touching any of the balls and lift it delicately without touching any of the balls. I've very seldom had someone ask me to re-rack it. Another thing that helps is when you're done racking before you put the rack up, put your hand over the balls and look for any spaces between the balls. The other player will take that as a sign that you're making sure they're tight (whether they are or not is besides the point - just kidding).