Walkthrough
There are several different ways to arrive at a successful conclusion in this story and (naturally) many more ways to arrive at an unsuccessful one. Of the successful endings, all are equally good. There is no one "best" ending.
Here are several ways to get to a happy ending. There are actually many more ways than this, depending on the routes you take, but these will get you to all of the main happy endings using the most direct routes.
Method 1: The "Tina" Thread
On page 4, choose to checkout the nearby businesses. When Tina threatens you, try to reason with her. After Tina sees the alien, turn out the lights and stay hidden in the darkness. Then, after the girl (Morgan) gets killed, stay in the café and figure out why you weren't abducted. When you go to get more supplies, take the truck instead of your car. After the accident with the alien, get out of the truck and examine the alien's body before continuing on to Hypermart. Continue to the end, answering any more questions truthfully.
Method 2: The "Jack/José" Thread
On page 4, choose to go to the police station. Ignore the girl and continue on to the station. Do not let Jack explore the wreckage alone. It does not matter which button you press first. Once inside the wreckage, stand beside the door so Jack can shoot anything that comes out of cockpit. When you get to the panel, you will see 6 buttons arranged like this:
123
456
Press them in this order: 5,1,3,4,2,6. Press the new button that appears. Continue to the end, answering any more questions truthfully.
Method 3: The "Morgan" Thread, Version A
On page 4, choose to go to the police station. Follow the girl. At the convenience store, choose to go to the police station and follow the rest of the instructions in Method 2: The "Jack/José" Thread beginning with "Do not let Jack explore the wreckage alone."
Method 4: The "Morgan" Thread, Version B
On page 4, choose to go to the police station. Follow the girl. When you get to the convenience station, take Morgan to her house. When you are attacked by the alien, go to the kitchen to get the gun. Go to the police station after you escape. Investigate the forest behind the police station on your own. It does not matter which button you press. Answer "yes" when the game asks you about the gun. When you get to the panel, you will see 6 buttons arranged like this:
123
456
Press them in this order: 5,1,3,4,2,6. Press the new button that appears. Continue to the end, answering any more questions truthfully.
Method 5: The "Morgan" Thread, Version C
On page 4, choose to go to the police station. Follow the girl. When you get to the convenience station, take Morgan to her house. When you are attacked by the alien, make a run for the front door. Reverse the car as fast as you can to throw off the alien. Go to Denise's house. When you get to the keypad, type the number 8362. Send an e-mail to the address given or simply answer "yes" when asked about the meeting. When you get to the meeting, type in the password NEDRA. Continue to the end, answering any more questions truthfully.
Method 6: The "Morgan" Thread, Version D
On page 4, choose to go to the police station. Follow the girl. When you get to the convenience station, choose to drive around and look for survivors. Go with Gunslinger. Continue to the end, answering any more questions truthfully.