If you are absolutely new to guitars, may I suggest that you do not try to buy one from a shop all by yourself? A musical instrument is more than what it looks like. The guitar of your choice may look like the most attractive instrument that ever existed, but at the same time, it might sound like crap. You, however, would probably not be able to tell the difference, would you? Therefore the first thing you should consider is not going there alone. Take a friend along with you, somebody who has some experience in the field and knows which instrument is a competent music maker and which is no better than a piece of wood.
There are a lot of little things that need to be considered when you buy a guitar. Despite its straightforward looks, it is not a simple instrument at all. And the toughest thing, when it comes to making a guitar, is getting the measures exactly right. That is why you should always go for a reputed make. You may have a thing for some local brand that has caught your fancy, but in view of your inexperience, you run a greater risk of being on the wrong end of the deal than if you played it safe and stuck with a known quantity.
First things first though. Do you know what guitar you want? Because a guitar is not just a guitar it is a genus. It is a class to which belongs lots of different types of guitar, of different sizes, styles and make. So, before you go to the shop and get your head all befuddled with the excess of choice, do some research about the types of guitar that are available in the market. If you want to play classical guitar, for instance, you have no business buying a solid body instrument. So, get some info about the type of guitar you aspire to master, and do not buy the wrong instrument.
There are a lot of resources available both on the web and in print from where you will be able to know your acoustic from your semi-acoustic and your electric solid body guitar from your four stringed bass guitar and how all these differ from the nylon string classical guitar and a flamenco instrument.
The trick would be to first decide which instrument you want to play. The styles are vastly different even if the basics are the same for each of these instruments. After you decide on the instrument, do not pick from the shelf the very first guitar you see. Go to the shop and play a little on the different guitars. If you cannot play even a chord, no problem, just hold it and get the feel of the thing. If you feel like its your instrument and if you feel completely confident with the beast, do not buy it yet, please. Ask a friend who knows how to play to test it out for you.
There are a lot of little things that might go wrong in a guitar, and you'd never know until it was too late. A fret might be set wrong. The action, which is the technical term for the height of the strings from the fret board, might be a wee bit too high for your comfort, the strings might be tighter than needed, and so forth. These may now appear to be minor details, but they will get magnified into really big problems as you learn to tell what is what. Guitar playing is actually very like rocket science, because a minuscule flaw can do the sound in a way that music degenerates into noise.