Not rinsing or soaking rice: Rice grains are full of starch and there is often a lot of starch sticking to the outside of the individual grains because they rub against each other in the bag. Starch becomes gummy when cooked, causing the rice grains to clump together. When you rinse out that excess starch from the rice, you automatically reduce all chances of clumping. Adding too much water: You need the perfect rice to water ratio when cooking basmati rice--or any other rice--and that changes according to the medium of cooking. If you were to cook rice in the Instant Pot you'd need less water than if you were cooking it on the stove. If you cook rice in the microwave you'd need more. Overcooking the rice: Cooking rice for too long makes the grains break down and become starchy, which in turn will result in gummy rice. Stirring the rice after it is cooked but before it has had a chance to rest: You need to give the rice a few minutes to sit after cooking is complete, because it will continue to steam during this time and finish cooking. If you begin stirring the rice with a heavy ladle during or immediately after cooking you will likely break the delicate cooked grains, causing them to become sticky or mushy.