Because I had it on the top of my mind when I read your initial post and then someone dropped it in the answers, it's this sort of mentality that is the reason I like to say that "Write what you know" is the worst possible advice you can possibly give a new writer. Never ever be afraid to write what you don't know, so long as you write it in such a way that your readers will thing you do (i.e. RESEARCH).
The fundemental flaw of saying "You never lived this life so you cannot possibly know" is betrayed by looking at the three best selling book series that were written with for children in the 90s-00s are Harry Potter by J.K. Rowling (Also doubles as the best selling book series that is not a religous doctrine (yet) of all time and to date the only series to net over one billion dollars in value), Animorphs by K.A. Applegate, and Goosebumps by R.L. Stine. Now, again, I'll remind you that these are books that are aimed at young males primarily in elementary and middle school ages and features characters that those readers can identify with. Of the three series, only one, the worst performer of the three, was written by anyone who had any experience growing up as a elementary or middle school boy. And even then, he featured girls as lead protagonists quite often despite his lack of experience being a girl. If you want to turn to television, which is dominated by male writers, then one of the most praised and scholarly critiqued television shows of the past 30 years is Buffy The Vampire Slayer, who's glut of strong female characters, television's first lesbian kiss, and humor are widely considered to be a high bar even after all these years... all created by Joss Whedon, a man who was never a high school cheerleader let alone a lesbian in high school in the 90s... but still managed to somehow give us some good ones.
You do not have to write about a character who meets your gender, sexuality, race, socio-economic situation, cultural background, or any other situation you don't know about. If your father was a hedge fund dude that no more qualifies you to being a great writer about hedge fund guys than it qualifies you to write about single parents on welfare.
"Writing what you know" helps you only to get comfortable with writing things. But if that's only where you stay, then you miss the point of writing (especially fiction). Fiction is the art of using lies to tell the the truth. After ally, fiction is not real, it never happened, and it might never happen... but if it's done well, it lead you to some places you've never been before, gives you perspectives you've never considered before, and opens up minds to new things. Consider the famous first interracial kiss on Star Trek depicted between caucasian actor William Shatner and African-American actress Nichelle Nicholes. Nicholes would later recall that she received more fan mail for that one scene than anything she ever did with Star Trek but her favorite came from someone who wrote in to tell her that he still was opposed to mix-marriages but, he did recognize that Nicholes was quite attractive and could see why Shatner's character would be comfortable with kissing her (and I am very much paraphrasing here. The letter is humorously backwards by today's standards. Given that the writers used mind control to explain why the two characters, kissed, with context, it could be reasoned that the letter's writer was calling BS on the out the writers gave to the accusation that Shatner's character wanted to do that... in effect, no one tells Kirk what to do and if he didn't want to kiss a black woman, he would have fought off the mind control and not done so.). Yet, in this example we see the power of fiction using lies to tell the truth: A man who admitted his own biases against interracial love was taken to what could be an uncomfortable place for his belief... and was able to recognize that the only thing "wrong" with what happened was the mind control... that's not real and real white people do kiss real black people all the time. Clearly no one is forcing to do it so they must actually find each other attractive and there's nothing wrong with kissing an attractive woman.
Like that example, fiction is not always going to keep the reader to a place they are comfotable with. But if you're going to lead your reader there, well, you got to first go there yourself.
Now, enough scaring the new writer... lets get you to some good resources:
I highly recommend TVTropes.org, but just beware it's like Wikipedia but WAY MORE ADDICTIVE. I'd say start with a look of their UsefulNotes section which are factual based topics on real life historical events, culture, religion, politics and political systems and unlike Wikipedia, a good number of them have some humorous wit to them. I'd also see what they have on various media depctions on things you're trying to do (they have sections on proper dialog, and sections on elements of fiction common to offices, traveling, relationships, and fantasy) AND SO MUCH FREAKIN MORE. Just give yourself some decent time, because if you're gonna write... or you're just gonna consume some kind of media, than there's a lot to read about in that site.
Personally, I've found dialog is typically incidental to the plot. I tend to plan events that need to happen, and when I need to do dialog, I wing it (unless the dialog is heavy heavy heavy plot critical... like "No, I am your Father" critical... then it gets planned out just a little more...).
I'd also let people read some samples and ask for feedback. I did that towards the end of high school. You'd be surprised how many people asked if you have any more... And hey, if you're not comfortable in social situations, that's going to make a lot of human interaction look wrong... because you're not comfortable with it in the first place... but remember, "Write what you know" is going to lock you into your comfort zone in writing... which is why it's terrible advice... and here's a secret about asking people who don't write: if you tell them you'd value your input and it's still a work in progress, but you'd like their input into your work... well... guess who's nervous... cause they can't write stuff... but you asked for their input into writing something which means you must think they are capable of writing to some degree... and they won't let you down. I've asked a lot of people to read my stuff in all sorts of terrible states... never once have I been given a critique worse than I give myself.