Hello, I am just testing MiG-21 and preparing some training missions, since it is a rather difficult plane to fly. Small mistakes can lead to fatal explosions.
Concerning takeoffs, I've seen that rolling on the runway at 350 kph or faster will produce the total destruction of the front gear, the plane nosing down and a subsequent nice and quick explosion.
However, you won't be able to takeoff with a speed below 300 kph. So, when rolling on the runway you have to take a close look to your speed, and as soon as you get 300 kph, you must pull back steady and quickly, so your nose get up from the ground and prevent the collapse of the front gear. Keep on pulling back, and you will see that you slowly begin to ascend. Maintain the joystick back until you are 100-200 m above the ground and your plane clearly begins to speed up. Then you can set flaps to neutral and rise your gear.
I've only prepared four training missions, but I will upload them as soon as possible so you can practice takeoffs, landings and interceptions. Take a look at the Campaign/Missions Jet Age in the next few days.
Good luck!