How do you get JV partners quickly?

I keep hearing that you've got to build relationships and not ask everyone you meet at seminars to do a JV with you, as you firstly have to build up the relationship.........this takes time and effort.....and you can only build decent worthwhile relationships with a finite number of people.

So, my 2nd question is - how can I build good, trust-worthy relationships with lots of people in a very short space of time?

Any advice would be welcome.