Because it is the second largest city in Thailand, getting there is no problem whatsoever, even if it isn't a usual stop for western tourists. The 3 best ways to get to to and from this city are by airplane, train or bus.
By Airplane
Hat Yai International Airport is located about 5 miles outside the city making it quite easy to get into the city proper once your plane has landed. You can get direct flights from Bangkok (both Suvarnabhumi and Don Muang), Kuala Lamphur in Malaysia and Singapore. There are also flights from cities in the U.S., Asia and Europe as well as domestic flights from most cities in Thailand. Because of the large Muslim population in Hat Yai there are also many direct flights to and from the Middle East.
By Train
There is a large train station in Hat Yai and it is cheap and easy to get trains here heading north to Phuket and Bangkok as well as south to Kuala Lamphur. The rapid overnight trains are a good bargain and if you can get a sleeper car you can arrive at your destination fairly well rested. If you are interested in a sleeper train you should contact the station in advance to book tickets as they can sell out, especially during Thai holidays and the Hajj when local Muslims will be making their journey to Mecca.
By Bus
Buses are the cheapest way to get around in Thailand and Hat Yai is no exception. You can get a bus from here to most of the Thai southern cities as well as Bangkok and also to the cities in Malaysia. The government buses run on a standard schedule and the rot air buses (air conditioned) are actually quite comfortable, at least for shorter trips. The rot thammada buses are not air conditioned and I wouldn't recommend taking them unless you really need to save the extra $10 that a rot air bus would cost you. In addition to the government buses there are also many private bus companies that can transport you almost anywhere in Thailand or Malaysia.
As you can see, getting to Hat Yai is quite easy and you have a wide variety of options depending on your budget and how quickly you wish to arrive. Likewise, you can find many transportation options leaving for points north and south. Traveling to Malaysia and Singapore by train of bus from here can actually be quite a bit of fun if you aren't in a hurry.
To learn more about Hat Yai and Hat Yai attractions please visit the authors website.