How do you hold rats?

I usually just grab them by the base of their tail when picking them up. Occasionally if I have to carry it far, I will hold it like a hamster.

All of mine a bread on sight and handled from day one. Usually when I popen the tubs they greet me at the entrance and are easily picked up. Most of my snake feed F/T so I gas them and freeze. :)

I pick up my 99% of my rats under their chest and bellies to support their weight. The not so social ones are picked up by the scruff or base of the tail. It's just safest method for the rat and keeper. You don't want to hand hold a freaked out rat who doesn't want to be handled.
And do not pick up rats by the middle or tip of the tail. Their skin or even tail can rip off.

Under the armpits by the chest, one hand. Rats hate being picked up by their tails (or at least mine do) they get hostile. But then, I learned how to read their body language and I've kinda trained them. I give them a verbal signal and room enough to say no.)