I changed my answer after @keithepley comment
#Post.find(:all, :conditions => { :approved => true })
Post.where(:approved => true).all
#Post.find(:first, :conditions => { :approved => true })
Post.where(:approved => true).first
or
post = Post.first or post = Post.first!
or
post = Post.last or post = Post.last!
You can read more from this locations
deprecated statement
Post.find(:all, :conditions => { :approved => true })
better version
Post.all(:conditions => { :approved => true })
best version (1)
named_scope :approved, :conditions => { :approved => true }
Post.approved.all
best version (2)
Post.scoped(:conditions => { :approved => true }).all