Having trouble getting your map ranked? You've come to the right place.
Precursor: Getting Your Map Modded
The first and most important step towards getting your map ranked is to get people looking at it - people willing to mod your map can be found in #modreqs, the modding queues subforum or by asking them directly after checking their signature for modding policies. Remember that all mods are useful - any perspective on your map can be used to make it a better one. Consider every suggestion a modder makes, and if you turn any down, post a detailed response in the map thread making it clear the reasons why. It makes them a better modder and makes you think more about how your map can improve! Also, if you found the mod particularly useful, be sure to give the post a kudosu.
Your map's star priority is important when it comes to moving on to the next step. If a modder particularly likes your map they might give it a kudosu star - the more you work to make your map better, the more likely this will be. You can also gain stars by modding other people's maps and spending the kudos on your own mapset. If you don't think you're very good at modding, practice makes perfect! Even a few small suggestions can really help another mapper out, so don't be afraid to give modding a go.
Once your map has been pending a while, has a relatively high star priority, and you think it's perfect and ready to be ranked, it could be time to call up a Beatmap Nominator. Make sure you check the team member in question's signature or userpage to see whether they have a modding policy: if they're open to requests or there's nothing there, ask them politely in game if they wouldn't mind taking a look at your map. Lots of BN are extremely busy — there are an awful lot of pending maps to get through, so don't be too disheartened if you are turned down. Having plenty of mods and kudos stars on your map will help encourage BN to look at your map, so if you're having difficulties throwing a few more kudos stars your map's way might improve your chances. Once a BN has modded your map and you've made the fixes necessary, call them back to take another look and see whether it is worthy of a bubble.
Just because your map is bubbled doesn't mean your work is over! Don't ignore any mods by normal users on your bubbled map — although only a BN or QAT can rank your map, anyone can still help improve it, and a better, more thoroughly modded map means an easier job for the BNG who eventually looks at it. Once you have applied a mod on your bubble the BN who originally gave the bubble will almost always be happy to come back and reinstate it. Keep in mind that you'll also have an easier time getting your bubble noticed by BNG members if it is high priority and on the first page of pending - giving your map some kudos stars to push it up in the list should make the wait a little shorter.