My family members are prone to dropping their iPhones and cracking the screen. I’ve gotten pretty good at replacing the displays myself, saving a lot of money over the price Apple charges (not to mention not having to wait a week or more for Apple to complete the repair).
As you might imagine, the screws and clips in an iPhone are tiny. If one of drops to the floor, you will never find it again. I bought this iFixit Pro Magnetic Project Mat and it does a great job of keeping all the fasteners in place. It has a dry erase surface to take notes and a square grid pattern so you can organize the components in a way that makes sense.
This weekend I used it while replacing the battery in my daughter’s iPhone 5s (it wouldn’t hold a charge for more than an hour) and it worked beautifully. It has a non slip foam back, which keeps a nice grip on the table. Amazon sells a cheaper magnetic project mat, but I don’t know if it has the same kind of foam backing)
By the way, iFixit has a lot of great videos and PDF guides for repairing many different kinds of electronic gadgets.