So, in order to add to some already really nice answers, here are my 2 cents on the subject. Take in mind, though, that I'm just like you in this regard- being naïve and well too much honest. So this is gonna be (I hope) a nice place to start.
Manipulate them through their wants
Every person wants something. Some of us want power, or influence, or true love, or knowledge, but all of us want something. A great manipulator knows one's wants while also knowing how to utilize them.
Stage 1, Learn: This is a lot easier than it sounds. Listen to what the characters around you talk about. Learning about their aspirations is not that hard when they will usually talk about things that they wanna do in the future. Listen to those conversations closely and record the things that pop from there, the things that come up. After a short while, you'll witness that some things come back up again and again. Those are the goals and the wants of the PCs. This is the key.
Stage 2, Suggest: After that, start a conversation with one of the PCs, in which you're gonna to suggest that you "may" know how to get, how to achieve one's goals. Something like:
Hey, Lisa, how are you today… You know, I couldn’t not hear what you said yesterday, and you know what, I think that, you know, just maybe, I… I have something to help you, you know the type, knowledge and the like. I mean, I think that it may help you, but… I'm not sure, you know, but it probably can be. You're looking for this tool, right? So it will surely be helpful to you…"
It doesn't have to be that long, or complicated, but a little bit of a slippery talk, with enough self-contradictions to not promise anything while still making it sound like there is something in there.
Stage 3, Ask: It is not enough to suggest that you may have the solution. You also need to get something in return. You need something, a payment, for all of your hard work. And you want at least some of it before you even give something.
Stage 4, Swindle: After you've got your payment, give a long solution to the problem, or a not-so-useful-info. You've got your reward, so no reason not to. Then swindle the character to another thing, make them forget this little thing, this little incident. Give them another bone to chew.
Yeah, in order to get that hammer of yours, you have to… I'm so sorry, but it's gonna be hard, you know, you… we'll have to enter this mall, you know, 'casue the shadowy figure who knows the way to the tool? Well, he needs some payment also, and he likes only a certain kind of payment so we'll have to look for it.
That's the idea, learn-suggest-ask-swindle. You learn what they want, suggest that you may be able to help them, ask for payment in advance and then swindle them away from it.
Squeeze emotional edges
Sometimes you'll have some emotional edges on other people. They may owe their lives to you, or maybe you just helped them greatly, or maybe you sacrificed a lot to help them in one way or another. You can use that two. Ask them for something, "a simple and small and tiny favor as a thank-you gift" or something. Or just remind them constantly that they owe you so they shouldn't do anything that somehow can hurt you.
Remember that time, a few months ago, that I left the concert that I was in the middle of (the one of the Stones, you know, for which I paid 100 bucks) in order to come to be with you, and you just left the minute I came? And now you're gonna do it to me again?
That's it, and you force this character to stay with you, 'cause she can't leave you again. She did it once, and you're squeezing the guilt that controls her.
Hint at things
The last trick that I use is hinting. People are prone to making huge things from tiny hints and using it to your advantage can save you a lot of headache later.
Remember how Lisa left early that day? I don't want to say bad things about her, but I've heard that maybe, just maybe, she's… no, it is too terrible. I think that I heard her, that I saw her talking with that enemy of yours, what was his name again? Olivia? Yeah, Olivia, and I think that they shook hands at the end. Yeah, it was here, a few meters from your front door. They were smiling, and Olivia looked at the door a few times, only for a second, only till I noticed her.
Again, the trick is to do as little as possible, make the hints as small as you can, with enough details to make the engines start rolling but not much more.