I know its second nature to most people on here to fit these but i did it at the weekend and took pictures as i went so thought it might help others if i did a bit of a how-to. This is only a guide and it might not be 100% correct but it seemed to work for me so:
You will need -
Your over-rider and corner bar kit with all fittings.
Masking tape
Pen or pencil
Drill with various drill-bits 3mm upwards
Sockets and spanners
Patience
Step 1.
Take your over-rider and your corner bar and assemble the 2 using the correct bolt and washer. Then trial fit onto your bumper and when you are happy with where the corner bar and over-rider are sitting attach the over-rider to the bumper (just finger tight at this point) as in picture below.

Step 2.
Take some masking tape and stick it on your bumper underneath where your corner bar is going to be fitted. It should be easy enough because the corner bar will sit off the bumper a few mm so you can slide it underneath as in picture below. Once you have the masking tape on there take a pen or pencil and draw around the corner bar. As in picture below.

Step 3.
Take your over-rider and corner bar assembly off and place safely to one side, take your pen again and mark off the centre of the oval you have just made when you drew around your corner bar. Then get your drill and put a small drill-bit in there to drill a pilot hole. I started with a 3mm bit. Take your time and dont be too heavy handed. Once through step up to a bigger drill bit, i think i used an 8.5mm but this was a bit tight but you can keep checking with your parts as you go. Its better to not take enough and re-do it than to take too much off. As below.

Then once have opened out the hole take the masking tape off. Dont do what i did and just pull it off and screw it up in your hand because it will have super sharp bits of metal shavings stuck to it that will cut your hands when you screw it up. See pic.

Step 4.
Re-attach your over-rider and corner bar, finger tight again, and put your bolt throught the spring washer and then through angled lump of metal thing. then slot that through your hole and into the corner bar. This took quite a few attempts to get it lined up and get it to thread in but be patient and it will go in eventually. As you can see for some reason my holes were in line with the bumper supports but these are pretty soft so i just bent a bit out of the way so i could get my socket on there. See pic.

Once done tighten that up and then tighten up the bolt on your over-rider and you've done your first one. Repeat steps for the other 3 corners

Voila.
hope it helps somebody
Sam