At modim, in shemoneh esrei, one bends the body forward without bending the knees. One should bend until about 45 degrees (the bones of the spine begin to protrude). One should not bow to 90 degrees (body horizontal). One should bow quickly. The head should be bent down as well.
One should straighten up before saying the Name of HaShem – the Name of HaShem should not be said until the person is standing straight.
The correct way to straighten up is to slowly straighten the head, then slowly straighten the body.