You can earn experience in Ranged 2K MT ability by simply taking on monsters and doing the damage they cause. The more you hit the more experience you'll earn in your ability. This is the slowest way to increase your level, but it is essential for novice players or for those who can't afford the more costly methods of achieving high levels.
The method involves the use of Dwarf Multicannon along with normal ranging. It's a quick method of training at low levels as cannons can reach 35 or more without requirement for ranged level. This gives extremely good performance and should be utilized by anyone who can afford it. You need to complete Dwarf Cannon quest in order to unlock it , and then pay around 1 million dollars to acquire each part. It also requires cannonballs, which can be quite costly.
It is mostly used by elite players due to enormous costs. Chinchompas red and Black chinchompas are ranged weapon/ammunition which is used to smack monsters on a the 3x3 AOE field. Through hitting multiple monsters the same time for huge damage, players can get amazing experience rates. This technique is usually used at Ape Atoll after finishing Monkey Madness 2 quest. It also requires high Ranged statistics since it's not recommended if your hits aren't high.
From the beginning of NBA 2K Coins level 1 all the way to level 28 you will need to use Darts or knives to increase you to reach your Ranged level. These might seem costly at first but they're not necessary to get higher. They are very precise and have great strikes and can be bought through Grand Exchange.