Always install the lower part of the glass first into the windshield gasket. I would STRONGLY encourage anyone looking to install their windshield themselves to go get a couple "windshield bones". These are plastic flat tipped installation tools that will make the job much easier. Since they are plastic you greatly reduce your chances of chipping the glass while using them. Stop into a auto glass business and ask if you can have/buy some old ones. I paid a guy years ago to install a windshield for me and he made it look so easy. He was kind enough to leave me a pair of "bones" for the next car I restore. Now I just install them myself. Keep the gasket wet with windex as you slide along the tool working the glass into the gasket.