My daughter dropped her iPhone 4S face down, shattering the screen. It was a mess and unusable with all the sharp edges.
I followed the iPhone 4S Display replacement guide on the iFixit iPad app. Using the iPad app was pretty slick. I discovered that you could zoom into the images by double tapping the picture. This was pretty valuable given my eyes could use an upgrade for doing these type of microscopic repairs.
The guide was very useful and accurate. The disassembly and reassembly went as described. You need to be really patient with this repair since there are a lot of very small screws to deal with and an abundance of adhesive assembly.
There we a couple of areas that were very difficult. The biggest issue was the one screw securing the display in the corner near the headphone jack assembly. You can't get a #0 Phillips driver into the screw straight-on since there is a bunch of assemblies that are not removed during the process still in the way. I has to us a micro straight slot drive to get into the cross-recess and slowly back the screw out. Reassembly was about the same in this corner; very tight and lots of potential to cross thread the screw and strip the slot out of the screw.
Removing and replacing the Home button was also a surprise. It is secured to the back of the display assembly with adhesive tape. You have to gently try to scrape the Home button and the rubber spring off the old display without separating the adhesive from the rubber, which isn't easy. About half the adhesive stayed on the rubber, the other half on the display. This made for some time consuming work trying to reset the adhesive to the rubber. The Home Button eventually was attached to the back of the new display but the final click quality of the button is not what was before the repair and the button rattles a little more than it did.
I also had some trouble getting the old display to separate from the frame. I had to use a small straight blade screw driver to push at one of the lower corners from the inside of the frame to push the display out enough to get a plastic opening tool in between the display and frame from the outside. There is some adhesive used to hold the display to the frame, so you need to overcome that before the display will separate from the frame.
Otherwise, the repair was pretty straight forward. It took about 2 hours to do. I don't think iPhones were designed with repair in mind so you don't want to take it apart too many times since the screw and adhesive won't be in very good shape the second time.
I would recommend buying a new Hom Button assembly to use with your new display assembly. I think the quality of the repair would be better using new parts in this area.
I recommend buying a brand new #0 Phillips driver for the repair. It pays to have sharp, undamaged drivers so you don't wreck your tiny screws. I would also find the thinest #0 Phillips I could find for removing the corner display retaining screw in step 33 of the repair instructions.
I purchased a Pentalobe screwdriver for the bottom back case screw, which made that part easy. I also got a Magnetic Project Mat which helped keep everything organized, which could have been a major issue given the number of small parts you have to deal with.
I also brought the replacement Phillips Bottom Screws, but I think with a good "Pro quality" pentalobe driver, you wouldn't need them.