1 - Choose a day and pray specifically for future priests (they have a link for 140 character prayers in several languages).the "#futurepriests" thing is to add a tag to all the posts so that they can be assembled. Sadly, but not surprisingly, some people have posted silly or nasty messages using the tag so if you are on Twitter go over and post sensible and prayerful messages. (They'll get tired soon enough.)
2 - Post a Tweet that you are praying for vocations and invite your Twitter followers to do the same. Use #futurepriests in your Tweet so we can assemble all messages related to the campaign on this website.
Take a look also at the dedicated portal set up by the Congregation for the Clergy, Annus Sacerdotalis.