The best way to be a successful translator is to sell oneself very well. You must indicate how prepare you are and how many experience you have, and, especially, to show sample translations in order potentianl clients can see your work.
On the other hand, you shouldn't say things like "I'm the best translator" or "You have to hire me because I'm the only person who can do your work" because potential clients will think you are bluffing.
Finally, the best way to promote you is being punctual with any job.