Imagine that you are seated in a race book in Las Vegas. How did you get there? Perhaps you chose it because of its comfort, efficiency and amenities. What would those be?
The first concern is whether the book is crowded. If so, check for the number of betting windows. It is important not to have to wait too long in a line to make a bet, as you could be "shut out" of a race. If the book is idle, look around to see if there's a reason why. The better race books are often occupied, even at off times.
Second, look for comfort and space. The ideal situation is a surface to spread out the handicapping materials and notes, and to have an individual TV screen to watch the simulcasts. There should be a wireless (or sometimes wired) internet connection for your laptop, if you have one. The number of big screens may make a difference to you, depending on what races you would like to follow. The big screens make it a little easier to study what is going on inside the race. Seating also should be functional and comfortable, as a lot of standing up and sitting down is involved.
Third, look at the board to see what races are being covered and if there are any other wagers or propositions of interest. Most of the bigger books have lines on all the races most people like to bet. But if you are interested in quarter horses, for example, or some specific kind of exotic wager, not every book may have them.
Fourth, with all that is going on around you, see if this is a reasonably serious and focused location to work on horse race betting. Some books are really parts of the casino. They exist because management feels an obligation to be a "full-service" Las Vegas casino. But there may not be a true commitment to the book. The ambient noise level is a good measure of how seriously "the house" takes the needs of racing fans.
Fifth, check out the food and drink if this matters to you. Some books comp the drinks to active players. Some have reasonably appetizing food, and others, well, don't.
It is a good idea to introduce yourself to the Book manager, particularly if you plan to do a lot of betting or to make reasonably large wagers. This may help with a comp or two in some of the older locations (that may not keep track of things electronically), and it may help you enjoy the best level of service the book can offer.
It is almost essential to enroll in the (free) player awards programs offered by the casino. This is the pathway to benefits other than just the winnings, and it provides a record of bets made. A fair number of casinos in Las Vegas are part of one group or another, which tends to make the various race books share similar approaches to their operation. (The physical look may reflect the "theme" of the hotel or casino, but the paperwork and procedures will be very much standardized.) Once you are comfortable with a race book run by Coast, Station, or MGM, the others in the family will seem a little familiar.
If this is a maiden voyage into horse race wagering in Las Vegas, visit a couple of race books before deciding what appeals to you most in the way of features and layout. Most seasoned horse race gamblers focus more on the personal service - the friendliness and competence of the personnel - than on the sticks and bricks or bells and whistles.