Xc traing tips help!!?

i am 14 soon to be 15 i did xc my time time for a 5k was 23mins but our corce is rellyrelly hilly its a relly hard to run but i relly want to be on varsity!!!!!!!!!!!!!! i have 1 month to train any tips will be nice also i have a bad knee! so any tips to deal with that will be nice too i want to get my time down to 20mins 19:00mins i am willing to train lol i got the eye of the tiger so anyhelp would be grate thanks<333333333