Most rats can become tame in a very short space of time with gentle regular handling. Rats normally only bite because they are frightened.
If the rat is a bit jumpy or nervous it is a good idea first of all just to get it used to your hand before attempting to lift it out of its cage. Try gently stroking the rat while it is in its cage and offering it pieces of food from your hand. It will soon realise that it has nothing to fear.
Next try placing your hand in the cage and letting the rat investigate, and step onto your hand, whilst keeping your hand still.
Once it is happy that there is nothing to fear, take off the top of the cage if possible or open the door of the cage, and gently scoop the rat up in both hands. Do not hold it too tightly or squeeze it as this may frighten it. Do not pull or lift the rat up by the tail.
Dont lift your rat too high as if it jumps from your hands and falls it may injure itself. It is always best to handle your rat whilst you are sitting down so that if it does jump it does not have far to fall and will simply land in your lap.
A good way to get your rat used to you is just to let it sit in your lap and stroke it. Many rats enjoy this and also enjoy a light rub on the head or behind the ears.
Once you have taken your rat out of the cage, and are sitting, face the rat towards you - they seem less inclined to jump if facing towards you and are more likely to explore its new owner by climbing up their body to their shoulder. If your rat does attempt to jump, let it and then simply pick it up again. It is better to do this than try and hold onto the rat which may cause it to become frightened. Once it is happy to step from one hand to another, gently start to curve your fingers around its body so that it can begin to get the feel of being held.
Before long your rat should be happy to walk from one hand to another with your fingers wrapped around its body and you can then start facing it away from you whilst you are sitting down and letting it walk again from one hand to another.
Some rats are more nervous than others and may take a little longer to become accustomed to being handled. Be patient and gentle and your rat should become very tame.
If your rat is really frightened or has had a bad experience being handled and bites whenever handled, try handling it whilst you wear a pair of gloves and handle it as indicated above. The wearing of gloves will help your confidence which in turn will help the rat. Once the rat stops biting you can move to handling the rat without gloves.
Younger children should be supervised when handling rats as they may unintentionally squeeze a rat, causing it to nip or injuring it.