'Design' and 'Shape' is the first thing that comes in the mind of a Smartphone buyer specially the novice ones. The design factors of Apple have always been a huge success and I hope that they will keep the new iPhone really simple and elegant like the previous generations of iPhone. It might b more sleek than iPhone 4s and 3Gs if the screen size increases. The next and the most noticeable change will be the removal of Apple's Trademark "Home Button" with make the iPhone different from all the other smartphones but because of this Home Button it also loses it "Full Touch" thing and hence becomes a semi touch Smartphone as in Android Smartphones the bottom edge of the mobile has touch gestures such as for changing brightness and theme etc. The removal of Home button might make it difficult to differ the iPhone from other smartphones as some smartphones have copied the structure of iPhone.
Hardware is the region of a smartphone which informs about how much power does the mobile contain and till what extent can you push the device's CPU and GPU. The new iPhone will probably have a better camera if not then obviously the previous camera. If they put the new Camera then it might be of about 12 MP. There might be a stereo speaker with subwoofers and a 20 watt amplifier like the iMac. The improved camera and speaker might increase the thickness of iPhone 5 which we don't want because then there will be nothing new in the design area. But the camera can still be improved by increasing the screen size and spreading the glass more thinner which improve touch sensitivity also. iPhone 5 might also get an Apple A6 processor with a capability of 1.2 GHz or more and also 1GB of RAM.
The thing that influences a smartphone the most is its software. Nowadays everyone is concerned about which operating system does a particular phone have either an Android, iOS or Windows Operating system. The iPhone will obviously have iOS and Apple will never put any other OS in its devices. The software is also same but there might a few difference in the UI of some internal apps like the Calendar, Mail, Music, Videos and Camera Application just like the new iPad has some UI differences. For other software thing there is nothing new as the iOS App Store is growing bigger and bigger.
This is the thing which every smartphone is given carefully, "Price". The price of a smartphones matters a lot. Although price cannot determine whether which is the best mobile but seriously people think more of price than the features and thats why Apple might cut of the price of iPhone 5 to make it the cheapest iPhone ever. It's price might be at about $499.