I would recommend starting with either the easiest piece or the piece that will keep you most motivated to carry on. I started with the helmet as the most iconic part. However some people leave the helmet to last as they want there skills to improve before they do it.
If you're ready with your glue choice and you have your craft knifes then the easiest way to start, is just to start, I use a 15cm metal ruler to make sure my cuts are straight, then the back of my craft knife to score the edge, some people use coloured pens, one colour for valley folds and a different colour for mountain folds. If you have the pep file up on a laptop if possible i find it helps to check what you are doing and helps locate pieces quicker to cut out.
The last bit of advice is to keep a build thread and post progress and questions, that way you help people in the future doing the same you.
Good luck