There is only one rule

Ok....here is my summary of 25 years of software development. Go Small.

Agile, Waterfall, Xtream, functional it does not matter the key to making any software project succeed is going small.  Someone needs to be able to break the project down into parts small enough that you can see the schedule slip.  It is easy to say....go do this.  When the this needs to be able to be done in less than 12 hours and then reported on.  If it is bigger than that and can not be "Done" in 12 hours then it is too big and you need to rethink it.