Well, first of all start doing it here. Check a few examples at the announcements threads. Read...read...read...and read more. With time you'll learn a lot.
Buy signature links! Make special offers, of course your directory has to be good or it will be ignored.
http://www.avivadirectory.com/strongest-directories/ IF you browse around youll find many more... that one is my fav even though i havent submitted my directory to it yet, ill do it at the end of the week ;p
1. first, announce your directory in DP, V7n solicitations section. 2. next, use a signature link and participate in forums. 3. submit to other directories or buy PR links. 4. submit your directory to directory lists (especially directorycritic / vilesilencer). 5. send a press release announcing the launch of directory. All you need just a good start. Good luck!!!
Do something newsworthy. Don't just launch - launch with style. Put out press releases, advertise with a decent budget ($10,000+)
Yes, sponsor a few sites... I can name some, not only mine. **Now Completly off-topic** Now you have a really nice looking avatar BritishGuy!
Something else - get people involved. I really liked the way Loren Baker launched Umdum. He got lots of high profile SEO people and bloggers to blog about the directory. It got strong linkage and good traffic from day one.