There are many ways to get an image accurately transferred to paper for drawing or painting. One which works well when you're wanting to enlarge your image is the gridding method. This involves drawing equal numbers of rows and columns on your reference photo and your paper then accurately copying the contents of each square. It's the method I use to draw my detailed pencil portraits.
I enjoy working out the dimensions of my proposed artwork and calculating the size of the squares etc but I realise not everyone gets as excited about maths as I do so I have devised a method which doesn't require number crunching. All you need to be able to do is to accurately fold a strip of paper and draw a straight line with a ruler.
I wrote a blog 3 years ago describing this technique, but it can be a little confusing to put into words so I promised I would make a video clip to show how it works. It's taken me a while but I've finally done it. I hope you find it helpful.