Well, 1st time I attached I put the tape on one way - and then decided I could get it even tighter by doing it differently.
>1 1st make sure there is no paint overspray on all the inside surfaces of the spoiler where you will be putting the tape, clean areas well with rubbing alcohol, clean area on front bumper as well. If you leave any overspray on - the tape will stick to the overspray at first, but then, because the paint is not adhered well on backside (at least it wasn't on mine because they didn't try to paint the back), the tape will pull off the oversprayed paint it is attached to easily and become detached from the spoiler.
>2 Cleaned the countersunk area of the spoiler that runs up & down (vertically) right behind the lip that goes around the wheel opening on both ends and then attached 3/4" wide 3m tape in that area both sides.
>3 Cleaned the top edges of both V's that cover the middle posts on the bumper & then applied 3/4" tape along the edges 1/8" down from top (horizontally) on both long leg and short leg - both sides.
>4 Tear off protective film from all tape
>5 Started at left side (looking at car) attached spoiler with edge tight up against wheel well opening, and while slowly wrapping the spoiler around the car to the right and making sure it fits correctly around foglight and grill - pushed the taped end tight to affix tape to car.
>6 When I got to 1st V center post (PS), held it out from car slightly, pulling back on rear edges of both long leg & short leg to spread the V apart, pushed V tight UP against bumper as far as it would go & IN on very point as fas as it would got - then pressed from pointr back along each leg to affix tape to car
>7 Repeat step 6 for DS V
>8 Worked my way around to right side end and then repeated step 5
>9 After I was sure all tape was affixed well I pulled the underneath of spoiler to match up the holes to the existing front bumper holes and installed/tightened the screws. I seem to remember that I had to actually find slightly longer screws than the factory ones for a couple of the holes because the original screws where made to only go thru 1 thickness (front bumper) and were too short to got thru both spoiler & bumper and engage in cage nut.
Hope this explains it well enough - good idea to do this after the spoiler has been setting out in the sun for a while to warm it up and make it more flexible.
2009 328ix E92//SGM//ACS Roof Spoiler//MTech Aero Lip+Trunk Spoiler//M3 Side Skirts//CF Roundels+Grilles//M3 Novillo Interior//Perf Shift Lever+Boot//MPerf DCT Wheel//M3 GT3 eBrake Handle+Boot//ACS Pedals//M3 Mirrors//LCI Tails w/LUX Rev//LUX 160 AE+MTec 6000K D1S+HPB HID 6000K Fogs//HPB LED Interior//RPI Scoops//CF Euro Airbox+Underhood Hsgs//K&N//BMW PE//MTech Rear Bumper-iS Sport Diffuser//CF Strut Brace//Vishnu OFT//BMW 193M's+Kumho 4X