What exercises help your running endurance?

I’m a beginner at cross country so i cover at least a couple of miles a day, but i’m having trouble building my endurance, and I feel extremely uncomfortable when I run. What is the correct form for running? Also, are there any type of workouts or diet plans that i could do alongside my running to help strengthen the appropriate muscles?

Cross Country training…how to make my run times faster?

I am a high school sophomore and last year i went to state in Cross country (running)…but this year i have tried to train and diet like i have been told, even maxed out weight ive never been able to, but the problem is–my mile times are exceptionally slower and its about to get me kicked off the varsity team…any advise in diet plans, training, sleeping patterns etc. to help me out??
thanks(:
~brittany~