I'd say there are at least 4 common ways to get into college coaching. There are too many "I got lucky" situations to cover. Some of these have better odds than others at success.
1) High School Coaching: While this isn't necessarily a likely cross-over, you can get experience at the HS level and some college AD/hiring committees will view this as good experience. You can actually make a living while getting experience if you are an ed major. The crossover doesn't happen often, but it does occasionally.
2) GA positions: These are getting harder and harder to come across. Many of them are now "interns" where you get paid 16k for the year without the option of getting your graduate degree. I know many people who came out of this type of position and scored paying jobs, but you will be an indentured servant for at least a year (and probably longer).
3) Assistant jobs: I'll split this into two types... A) Paid. Good luck with this one. You may know someone who can hook you up, but unless you're a connected individual there is not much hope. Without coaching experience it is really hard to get a paying job offering coaching experience. B) Volunteer. Most people I know who got into coaching either did this or the GA/intern route. I recommend a couple ways to narrow the field. First, check programs you know and look for some clues on their web site. If they have almost no coaches listed (ie, if the head track is listed as the assistant cross and you know this team has a huge number of athletes), the XC coach could be starving for help. This is how I got involved. Also, if there are a veritable ton of coaches, the coach could be grateful for any assistance offered. Second, talk to people you know about coaches that may need help. It can be well known someone is in over their head. Finally, get a list of NCAA institutions. There are lists of all NCAA (or NAIA, whatever) schools offering the selected sport. Sometimes the neglected programs you've never heard of offer good opportunity, even if it is to get experience and then move on. Check to see if a coach is filling multiple roles (ie, soccer and track or something). Also, look to see if the contact e-mail isn't from the school. This is a huge red flag, and it does happen. In either case, contact the coach because they could want help or some relief from other tasks.
4) I highly recommend getting a graduate degree. If you go to grad school at a place you've talked to the coach about volunteering, it can work out well. Chances are you'll be working hard for whatever grad degree, but helping at practice a couple days a week can give you a good reference and put your name with some success. It's kind of the GA thought, but you back your way into it. Most schools look highly upon a grad degree regardless of subject. It's one of those hoops to jump through, but it can pay off.
Build a network in whatever you do. Sadly, it's the most useful tool you'll have. Even if you don't know a specific person, you'll be shocked at how incestuous the coaching field is. A call from someone they know can make a difference.
I mentioned it before, but coaching doesn't pay to start, and you're really lucky if it does. You'll probably have to find something in addition.
It's best to learn names, hold a stopwatch and learn how the coach works before even thinking about advising the athletes. If an athlete wants to chat about training, the answer is always "ask what coach blahblahblah thinks". Only start doling out advice and doing more active coaching when you are given the go-ahead to do so. it's what I did in my first gig. I developed a great relationship with the head coach, so he knew my advice was sound. The athletes (in our conversations that didn't end in "go see what the head coach thinks") started to like me as well, and it wasn't long until I was a full fledged addition to the squad. BUT, you have to wait and learn...
You may have to string several of these together. You may start as an intern somewhere, volunteer somewhere else, get a crappy assistant job another place and then 12 years into the process find something you like.
Regardless of the approach, expect to send a lot of e-mails, make a lot of calls, be rejected many times and flat out ignored more. There will be times where you think "what the hell?" on why hiring decisions are made. People far less qualified and competent than you will be hired. It sucks, but move on.
Have fun...