Freelance speech writing is the champagne of freelance writing; it offers a high degree of creativity, a high-profile clientele, and the chance to have your work heard among elite people. Of course, there are downsides as well: your style is restricted to that of the speaker, and the pool of jobs is substantially smaller than many other forms of freelance writing. But on the whole, the advantages make it very attractive to pursue gigs as a freelance speech writer.
Speech writing is one of the oldest forms of communication. Much of what we consider good rhetorical practice today goes back to the Romans and Cicero. Until the previous century, long rhetorically-polished speeches were a central (and enjoyable) part of serious literature, from the hieratic diatribes of Shakespeare's Lear to the long burlesque flights of Dickens's heroes and grotesques. Today, speech writing is mostly confined to large formal parties, serious events, and political careers, but something of the dignity of the art's long history still adheres to people's ideas about roaring good speeches. Speech writing is the art of making people appear both persuasive and dignified, of turning ordinary people into sources of entertainment and wisdom. As expected, writing speeches effectively can be difficult to do well.
The key to effective speech writing--as well as the key to effective writing in general--is to know one's audience. In speech writing, the audience is a literal one: an employee pool, a group of wedding guests, or a rural electorate. The speechwriter should, before setting even one word to paper, find out who the speech is intended for and take this into account when structuring the work.
Once you know your audience, know your speaker. As Bernard Shaw once said, it's impossible to make a silk purse from a sow's ear -- or at least, people don't want to believe it's possible. If the CEO you're writing for is known as a good ol' boy, down-to-earth businessman, it won't ring true if your speech contains a number of high literary allusions and elaborate rhetorical constructions. If you're writing for a museum curator, opening with an off-color joke and referring to "the folks back home" is not necessarily the best way to go.
You not only have to know about your client's perceived character, but about his or her actual speech rhythms. Interview your client if possible, or if not possible, try to get access to videos, tapes, or other recordings. This should give you some idea of voice, and some understanding of how best to express your ideas in the "client's words." If a speech doesn't sound natural coming from the client's mouth, the speech won't work and you won't develop a good reputation that leads to more assignments. So put in the time, get a good idea of the client's voice, and use it exclusively in your work.
Framing your speech around the subject matter can be tricky, but fortunately all the prep work you've been doing will make it a much simpler proposition. If you know your audience, your client's speech style, and your client's public perception, you'll have a decent compass for navigating your speech through possible dead areas, out of dark, depressing moments, far to the lee of excessive frivolity, and generally on an even course from the first attention-getting moment to the conclusive point. It's difficult to know exactly how a speech will play before it's actually delivered, but you can get a rough idea by reading your drafts to a friendly audience (spouse, friends, children), or by tape-recording yourself delivering the speech into a mirror. A good speech doesn't have dead moments, doesn't bore, and reaches a series of short, conclusive points to keep the audience's attention from wandering over time. If you do plenty of revision work and get a real idea of how your speech sounds when read aloud, you can fine-tune appropriately in order to ensure a successful speech, and a satisfied customer.
Of course, getting customers in the first place can be tricky: the speechwriting market is usually fairly small and fairly exclusive, since only the very wealthy can usually afford to have professional speechwriters work for them. The Catch-22 here is that the very wealthy typically only want established, proven speechwriters, a difficult preference for novice speechwriters to deal with. You can establish yourself and build a reputation, however, by advertising heavily in local papers, club newsletters, and anywhere likely to need a speech writer at some point in time: wedding planners, local organizations, startup corporations in your area. This may not be the best-paying work, but it's essential to building a proven reputation as a good speechwriter. Once you have some gigs under your belt, start upping your level of advertising to include corporate newsletters and trade journals, and make sure to network at every event where you've written a speech. Word gets around, and eventually, if you promote yourself well, it'll get to the right people.
In any case, it'll be some time before your speech writing is well-known enough to command high prices, and to allow you to make it the exclusive focus of your freelance writing career. Keep up some other freelance jobs, write speeches whenever you get the opportunity, and keep up the self-promotion among the right circles. If you're talented and you're fortunate, you can make the switch to the champagne of freelance writing, and achieve that most satisfying of jobs: you can become a successful freelance speech writer.