Took a while but I finally got my head round how an insects legs move when it walks. I've only used six of the eight legs as actual legs for my spider with the other 2 becoming arms at the front - they'll be shorter and hang from the front of the body.
I looked at videos of spiders and also at how the spider in James and the Giant Peach was done. The body doesn't bob up and down instead it stays at the same distance from the floor and moves at a constant speed with the legs moving rhythmically either side of it.
Next step is to include the legs on the other side of the body and to then add the big bum bit at the back and her head.