Well, that depends if it’s a real place or a made-up place.
If it’s made up, you get to make it up, so the important part is documenting what you make up. Draw maps, even if they’re just horrible sketches because you have no drawing talent. Mark down where you put each building in the town you’re describing. Keep notes about everything so you don’t contradict yourself later, from the number of windows on the library to the color of the grass.
You also need to remember that this setting should fit in the world you’re writing in. So if you are writing a fantasy world, go ahead and have blue grass. Just make sure that grass is supposed to be blue in this world. (And if you can come up with a logical reason why, even better!) If you’re writing a made-up town in the real world, you shouldn’t have blue grass. (Unless it’s Kentucky bluegrass, which is actually green.) But if you’re writing a made up place in the real world, you need to be sure everything fits with the real world. This will require some research, but you can probably take most of what you know about your town and extrapolate, and just check to be sure the principles are the same wherever you set your fictional place.
If you’re writing a real place you’ve never been, that’s much trickier. You’re going to need to do a lot of research. Start with Google Earth and view the town in street view. That’ll help you get the layout, building descriptions, etc. Once you have that, you need to find out about attitude, ambiance, etc. Every place is different. Even places where people are generally laid back or uptight are laid back and uptight in different ways.
The best way to find out about attitudes and places your character should or shouldn’t go is to talk to people who live there. Or if your character will be a visitor, talk to people who have visited frequently. Post on the internet asking for help. Someone will know someone who knows someone who lives/visits there and would be willing to email. Find the contact information on the area’s tourism info website, and contact them. Tell them you’re writing a book set in their city and ask if they’d mind answering a few questions.
When you call or email, have your questions ready. Be polite. And don’t be upset (or at least, don’t be upset publicly or take it out on anyone) if they can’t help you. Ask how they’d like to be credited in your book. If they say they’d like to be, be sure to include it.
Research the history of the area. Check out the chamber of commerce website to see what businesses are in the area. Look up local news online and watch the videos. Find out everything you possibly can about that place, so it comes through when you read the book.
If you’re a fangirl/fanboy, pretend that place is your favorite celebrity. You want to know everything possible about it, so you’re going to watch every single video you can find from there and about there. You’re going to read the quotes that come out from there. You’re going to research what it would take to visit there. And when you know everything you can, you’re going to write your story about there.
After you write the book, get someone from the area to look it over for anything that jumps out at them as wrong. Again, be polite and offer to credit them in the book.
It will be a lot of work, but it’ll be worth it in the end. People who live there will notice what you get right… and what you get wrong. Short of actually going there, extensive research is the best thing you can do.
And if you have the money to travel and live in the US, it would likely be tax deductible to visit a place to do research for your book. (Consult a tax adviser for details. I’m not one.)