Interactions with NPCs you meet in Fallout 4 are more limited than in previous installments of the series. After you walk towards a NPC and start conversation, you cannot select full dialogue options from the list. Each time, four various reaction options appear on the screen. They are assigned to various buttons on the pad or keys on the keyboard. It means that in some cases you must guess how your character will answer basing on a very short description. Reaction options very frequently have similar application in different conversations. Bottom option is usually used when you want to agree with your talker or accept to help him. The right option is usually used to end the conversation or refuse. The upper option is mostly used for asking additional questions. The last, left option has the most uses, but frequently it is used for giving sarcastic answers.
Simplifications in Fallout 4 can be also noticed when using main character's skills during conversations. In difference to, for example, Fallout: New Vegas, specific perks do not unlock new behavior options in conversations. The only character trait that can directly impact the conversations is Charisma. It allows selecting special behavior options that are marked with yellow, orange and red color. These options can, for example, discourage NPC from battle, make him give you better reward or allow you to obtain additional information from the talker. However, it will happen only if the persuasion attempt will end successfully and if you are lucky, as every time you use these actions, the outcome is generated randomly. Due to that, it is a good idea to save your progress before each important conversation, even if charisma of your character is very high (8-10) points.
Important - A successful persuasion attempt is each time rewarded with experience points. It is an additional encouragement for using high charisma in conversations.
Important - Some perks and magazines you find are slightly related to perks as well. As for the perks, you should take interest in Woman Killer that increases chances for persuading women. In case of magazines, Live & Love issues should be interesting for you. Selected magazines of this group give you additional experience for using persuasion.
Meeting with merchants in order to save unneeded items or buy their goods is a separate category of interacting with NPC. During the conversations with the merchants you cannot use Charisma directly, but its current value will impact the prices of bought and sold items. If you plan to trade frequently, you should be interested in perks from the Cap Collector group. Two first levels of this profit will improve the attractiveness of prices when buying and selling. The third, last level will additionally "equip" the merchants with more bottlecaps. It is very important, as each merchant has limited number of bottlecaps and it forces you to "juggle" between merchants or depend on direct trade of goods (for example, commodity A for commodity B instead of commodity A for bottlecaps).
In addition to unlocking the Cap Collector perk, you should also obtain magazines related to trading - issues of Tales of a Junktown Jerky Vendor. You should collect as many of them as possible early in the game.
Important - If you don't want to overpay for merchandise or get rid of your own items for small money, postpone your first "serious" trading visit until you unlock at least some of perks and magazines described above.
Important - You can try stealing from any character you meet in the game. This unique interaction type is described in a separate chapter of the guide (Sneaking up and pickpocketing chapter).