Like most endless running games, play takes place in what is known as a 'lane'. There are in fact three of these, helpfully indicated by train tracks on each one. The game will throw various obstacles at you, including moving trains, signposts, dumpsters, tunnels, bridges, buildings - pretty much anything you could imagine to make your life a bit more difficult. Because there are only three lanes, you have a very straightforward role: pick a lane for the upcoming obstacles.
Now, you will often have to be looking at the horizon of the screen, trying to see what obstacles are coming up and working out how best to tackle them. As you stay alive for longer in each level, the obstacles will get harder. The game facilitates this by putting obstacles close together, and by requiring more complex moves to get past them. For example, you may have to dodge to the right then instantly back to the left to avoid something in your path.
You can see how lanes work in the image below - each track is in a different lane
Unlike conventional gaming, endless running games are just what they say: endless. This means you are getting great value (although the game is free!) as you could potentially play one level for an unlimited amount of time. Players can compete for scores and time, rather than the achievement of beating a particular level. Moreover, there are challenges to complete which require and characters to unlock which require a lot of dedication and many hours spent playing. These factors, plus the fun gameplay and frequent updates, combine to keep people coming back for more.
A good tip for beginners is merely to spend a lot of time on the game learning the patterns of obstacles. Everything is randomly generated, so no two runs will ever be the same, but you will often find multiple obstacles grouped together, certain sections repeating themselves, and various advanced maneouvers required frequently. Similarly, while the shiny easter eggs or mystery chests may look tantalizing, it is often not worth risking your run just for the sake of picking them up. Don't be afraid to ignore coins and power-ups if you are on a good run just to stay in your current lane and not take any unnecessary risks.
The premise behind Subway Surfers is that you play a teen spraying grafitti on the subway. You are interrupted by a character known as The Inspector. Deciding to flee rather than face your crimes, you must run through the subway, dodging obstacles including moving subway trains, to evade your pursuer.