Entirely dependent on a given office's staffing situation and whether you do Admin, Leg, or Comms.

If you are super organized and have good 'customer service' skills being a scheduler usually provides the highest salary floor and good opportunities to earn extra from the Member's campaign side. I've seen people go from interns to schedulers in 12-16 months.

Leg is the "standard" route when you think of Hill staffers and you should expect 6-12 months per level *minimum* (Staff Assistant, Legislative Correspondent, Legislative Assistant) and then Legislative Director (LDs). I didn't know an LD making less than $100k.

Comms is probably the area where you can rise the highest the fastest. If you understand social media and can distill your member's message well I've seen press assistants (entry level comms staffers) go to comms directors in a matter of 18 months. This is role is probably the most member dependent in terms of responsibility and salary though: a sleepy member from a safe seat won't have the same needs as a conservative/liberal firebrand. Comms is also more marketable outside the Hill itself (whether in media, non-profits, or campaign side) so that can push comp higher.

Couple items I would offer:

-Being from the district can help your chances big time, but is certainly not mandatory for most offices.
-Previous campaign/organizing experience (NGOs, nonprofits etc) can be helpful if they are related to issues that particular MoC cares about.
-One of the easiest ways to work your way into a Member's orbit is to get on their campaign in a volunteer/staff capacity and then make yourself invaluable at the district level.
-Entry level pay is terrible, and doesn't really get D.C. CoL appropriate until you're at the LD/CD/CoS level.

But once you do get on the Hill, moving around is exponentially easier. There is a *massive* foot in the door effect (even moreso than other industries) and it's very rare to see a senior level staffer come in with no past Hill experience.