To become the head of a rank in this pack you must show that you are going to remain active and prove yourself in rp. Below is a list of the things you will need to prove you are able to do to gain your rank (remember that you won't always do everything perfectly and might fail every-so-often)
Hunter: Hunt prey for other pack members, especially if they need it. You must catch a number of different prey from rabbit to elk
Herbalist: Recognise herbs throughout our territory and use them to heal other wolves that need it. Just recognising what a plant can do or the best way to cure something will count to proving yourself.
Nanny: Help the mother with caring for her pups while she is still around, or any young wolf. If there are no pups or young wolves then show that you care for your fellow wolf and can tolerate any wolf.
Warrior: Assist in fights with other wolves, but if there aren't any then help resolve fights between wolves within the pack i.e. help split up fights. You could also demonstrate your strength by helping the hunters tackle big prey.
Beta: First you must have held a previous rank. After that you must show that you can help resolve fights (without violence if possible), can give sound advice to the alpha's and assist the other wolves if they need it.
The alpha(s) will decide if you have your rank and will tell you in role play.
Becoming the head of a rank means that you can tell the others in your rank what is needed to be done. Don't boss the other members around jut because you can otherwise I will take your rank away. Same goes for the Beta rank. You get to boss everyone around, and if something happens to the Alpha's, you are in charge.