Welp, the easiest way to be on good terms with the Enclave is to join them. That will give you +1000 reputation with them off the bat (and -2000 with BoS, and smaller positive and negative amounts for other factions, just thought you should know). After that they will enable you to walk into their base and trade with them, so it won't be as hard as defending their patrols from neutral reputation until 200.
After that you can maintain and strengthen your friendship with the faction by trading with it ($100 in goods exchange is 1 reputation point) and defending their patrols. Also do quests, provided they aren't glitched. Last time I heard, BoS and Enclave quests are a little difficult, but it might be because most people don't read the dialogues and then wonder what was the quest about that they accepted.
It's gonna be real hard to maintain over a long period of time because after your reputation crosses a 200 mark, it will drop down over time to that amount. And the same if it goes down below -200, it will rise up to that amount over a period of time.
Seriously, this information is in the wiki and if you would look for it you would have found it.
Good luck in your pursuits!