Well, Naturally, you'll want to rank up won't you? Here's how:
Genin to Chunin -> Simple, participate and pass the Chunin Exams, they vary every time so don't expect the same thing every time
Genin -> Special Jonin Simple as well, participate very well in the Chunin Exams, pass and show exceptional skill in a field, e.g tracking
Chunin/Special Jonin -> Jonin.: These are self appointed by Kage's when they feel you have done well enough to help the village
Jonin -> Kage: This is decided by a village wise vote, between the top three RPers, missions, Rp quality and the such will go into this, a topic will be made for voting. this will only happen when the previous Kage dies.
Sannin: To gain Sannin, all Kage's will meet up, in a neutral area, and decide on the top three ninja in the world, from any country, wherever they may be. this is usually decided on RP skill and quality of posts.
ANBU: These are appointed to the loyal members of the village, who the kage personally trusts. No bias opinions are allowed when decideding this
Missing Nin Ranks:
D Rank Missing Nin: No Requirment
C Rank Missing Nin: Kill Three Players or attack a village and do little damage
B Rank Missing nin: Kill Five Players or attack a village and do moderate damage
A Rank Missing nin: Kill Seven Players or attack a village and do a lot of damage
S Rank Missing Nin: Kill Ten Players or attack a village and almost destroy it.