This is the first time I have done it also.
We put some warm water in the basin and some Johnson's baby bath and then just put her back end in. I washed her, my daughter held her front half and at the same time we were giving her hugs and kisses. She was purring all the time and didn't seem to be bothered. We dried her thoroughly and we turned the heating on so she could be warm.
We thought it stop her licking her tummy (see my licking thread).