Firstly if you want your map to get ranked, it needs to have atleast 2 difficulties, the song should also be not too long and it shouldn't give too much score. It's also recommended that the difficulties are spread-out, for example; one Hard/one Normal or Easy, not one Insane/one Hard because newer players might have trouble playing your map, the result being your map won't be as popular.
Whenever you've completed those minimum of 2 difficulties and submitted them, get people to look into your map. If someone likes your map, they'll give it a
Star. I highly recommend posting in those modding queues, just make sure you read their rules, don't be excessively annoying or impatient(hell I never pmed anyone telling them to hurry up with my mod) and make sure to give them a Kudo if their post helped. Whenever a Map Assistance member finds your map to be good enough, he or she will give you a
proto-bubble (They will say that in their post, there's no symbol that indicates if a map is proto-bubbled). Once a Beatmap Approval member is aware of the proto-bubble, they'll eventually check your map to see if it's ready to be ranked yet, if they think it is, they'll give it a
Bubble and once a second BAT approves it, your map gets ranked.
Like 0_o and rust45 said above, it's all about how much work you put into your map. My first one got ranked in 2 weeks because I asked a lot of people to check it and made changes every day.
Hopefully this wasn't too long to read(probably was) and helped. Goodluck