The best way to pick up a rat is to scoop it up from underneath. You can put one hand or arm next to or in front of the rat, then use the other hand or arm to gently guide or nudge the rat in that direction. If you do it right, the rat will hop onto you, and run up your arm!
You should avoid grabbing a rat from behind because they don’t like that: it reminds them that they are prey animals, and could be captured and eaten. They will often squeak and try to escape or defend themselves.