
If you haven't completed the quest before or want the full story, you can start by going to the Covenant. The quest begins in the small town named Covenant and ends in the superb, mega, high-secret place called Compound. She is being a held prisoner in the secret object and is a part of the quest named "Human Error". The quest we are going to do is about saving a life. That is why we are going to earn max affinity by saving person’s life!

And that is actually what you are going to do because we are going to cheat a bit! We won't be retaking the Minuteman castle, as it features nasty fights with Mirelurks and their Queen! If you are fond of fighting those creatures you can go, however, I find fighting them completely unrewarding. You can tell that you aren't ready and want to prepare. Once you are almost the best friend of Preston Garvey he will tell you that he thinks it’s the best time to rebuild the Minuteman and retake Minuteman castle. These Companion chats can be delayed and started at the moment you would like them to, so I recommend to save before the chat and squeeze the maximum positive reputation possible. To earn some positive reputation from that chat, and not to lose any, you would like to be as supportive, of him, as you can. During the chat, he will tell you a history of Minuteman. But before that, as his affinity will grow he will be willing to talk with you few times. This is a point after which you will have maximum reputation earned with Preston. However, the settlement based quests are the quickest way to increase the reputation to a point when Garvey will ask you to help him complete the Companion Quest. Preston is fond of any generous decisions and quests. As you will be helping the settlements together with the Companion, his affinity will grow. Garvey has infinite amounts of those quests and settlements that need the help. After you've completed the quests Preston gave you, take new ones.

Now that you have Preston as your companion, it is time to earn reputation! The way I find to be the easiest is this one.

Once you've done that, Preston will be impressed by your deeds and will be happy to join you. He will ask you to lend a hand to Sturges and help few settlements. As soon as Preston will arrive there talk to him again. After you complete the quest head back to the Sanctuary. Don't worry! There is not much work to do! The first quest will be given to you once you arrive in Concord. And for that, you will need to complete all the quests that are available before he will want to join your crusade. First of all, you will need Preston to become your companion.
