One of the most important things that you need to keep in mind in order to become a great noob tuber is that maintaining a certain distance between yourself and the target is crucial. If you let the target get too close, you will have a hard time killing him. Therefore, it is best to look for a spot where you will not have to worry about the target sneaking on to you from behind or the sides and getting an easy kill.
Camping works really well while using a grenade launcher, as you need to keep close watch over just a particular angle. However, camping at one spot for too long can put you at a greater risk of getting killed, which is why you should consider changing your camping spot after every four to five kills.
Do not move around too much. Unlike a shot-gun or some automatic weapon user, you will not be able to move and at the same time aim accurately while using a grenade launcher. Therefore, keep your movements to the minimum. Consider moving only when you want to get to a camping spot, or when you want to shift to another camping spot.
Learn the map that you are playing on in order to become aware of all the possible routes that your targets can possibly take. If you keep your eyes open and mind sharp, it will not take you a very long time to get an idea about the route that other players take most frequently. This will allow you to get in position and be prepared to fire the grenade the moment you see a player passing through or exiting the route that you predicted them to take.
Remember the spawn points. You will be able to get really easy kills if you attack the players the second they spawn. There are more than one spawn points on a map, but you should not have much difficulty making a decision. Your preferred spawn point should be the one where you will have a good camping spot or a barricade to protect yourself from incoming fire.
Practice is the key to becoming a very good noob tuber. Forget about using other weapons for a while and simply concentrate on using grenade launchers to get your kills.