Its so nice to be needed
My man advice is to go slow and pull it as tight as humanly possible. That string is tough stuff, you can give it a ton of stress and it will not break, just dont over do it. The seams of the cover should come together making it look custom.
Oh and this may seem stuped to mention but when installing it make sure the seat is far back, you would be supprised to realize half way through that you could have been more confortable if you had done so. I also had the door open so that I could get a good look at it at every angle to make sure I didnt miss a hole or lace it through the wrong hole, one mess up can force a lot of un stitching to get it right.
Also when going around the forks try not to skip any holes, I dont think the BMW's wheel is so wide where that will cause a problem. Make it clean, if you notice going over one of the spokes that it would look better laced below it insead of over it then un thread it and change it.
Try to keep the seam on the inside of the wheel but dont worry if its not perfect. Despite how tight you will make it, the whole thing can still be twisted around the wheel to make it look perfect. This should never need re adjusting as it is very tight fit and wont move unless you give it great force.
My last word of advice is to not cut the string to short. It is very easy to leave a little left and then tuck it under the cover.
I think that covers everything, enjoy and be sure to post pics when done.