In general, I believe campaigns shouldn't manipulate the natural behavior of members. Allow everyone to post where they feel most comfortable or where their contributions are most needed, and then select them without revealing the reasons why. 
It's not possible anymore, most users already know the criteria without the campaign managers need to stated the reasons.Gambling campaign? I will post in gambling board.
Must earn x merits per month? I will catch merit regularly including ask help from friends/local members.
Don't burst post? I will wait at least an hour before create the next post.
Don't burst post(2)? I will spread the post everyday instead of post in the last two days.
The only way to know the true character of every participants is don't mention any rules from the beginning, but it's already too late.