"Conference speaking" is not a job or a target activity. You speak in conferences as part of other jobs/professions/lines of work, and as your reputation and success in your chosen line of work increase, more opportunities pop up. If you want to be a "conference speaker" as your end goal, honestly, you should prepare to become the butt of jokes. You'll come across like Greg Kinnear's character in Little Miss Sunshine.

There are a few basic types (I've done a fair amount of 1 and 2 below):

1. Academic speaking: if you are a PhD or a practicing specialist who is doing somewhat new things, speaking at conferences is a routine matter. You submit papers, speak at the commodity sessions and so forth. The smaller the conference, the more interesting it is. As you accumulate a pile of work, and/or do award-winning work, you'll get invited to do special addresses or even keynotes. You'll give seminars whenever you interview, and inside any organization you are part of.
2. Trade speaking: If you are in industry, and you are either leading high-visibility projects, OR are high up in management, you'll speak on behalf of your company at trade events. You may be invited to speak on specific themes or participate in panels, or give little thought-leader bits.
3. Consultant circles: "conferences" are a primary marketing medium for self-employed/independent consultants in many industries where a lot of the labor is outside of organized companies. Consulting companies often rely on conferences (often organized by themselves) to do most of their lead generation and marketing. Depending on the particular conference, this can be a highly backroom mafia affair, or a meritocracy. Speaking spots might be loosely or tightly tied to sponsorships.
4. "Professional" speakers circuit: these are people who have typically published at least one book that is relevant to a larger community. They get invited to do keynotes and moderate panels, and get paid for it. Big names like Bill Clinton get paid like $100,000 or more (that's the figure I heard). On the low end you get the 2k "budget" speakers to about 10k. Below 2k, the fees get dressed up as "honorariums" :). This kind of speaking tends to be the most meritocratic of all, since conference organizers tend to reserve these spots for charismatic speakers who have a crowd-pleaser story to tell. Big names can make or break a conference on the edge of mediocrities. Not all writers/pro speakers can do this. If their work isn't relevant to any community, they go on solo speaking gigs. Things like TED and Davos are obviously at the top here.

So the basic advice is: if you want to get into conference speaking, get good at something else. Preferably something with a popular side to it, rather than obscurely technical. If you DO do something obscurely technical, but it turns out to be amazing work, you could always get some help to turn it into a TED talk... though I dread to think of Einstein doing a TED talk. Horrible thought. Kills the romance.

And keep in mind you may or may not like it. Often people who do the kind of great work that can fuel great talks are the kind of spotlight-avoiding introverts who dislike conference speaking, and have to acquire a taste for it.