Remember Warner had played several seasons of pro ball in Europe and the Arena Football League. In most leagues, running backs are the hardest to find, and thus ranking them is the most important. Neither alone will bread a successful fantasy running back, but together they are a sure-fire combo. After that I consider the total quality of the offense, and then the quality of the running game. There are less backups turned stars at running back then at any other position, so I will rank fewer backups with the starters then at quarterback and wide receiver.
Wide receivers are very different then most other positions.
There are two starting on every team, and most teams run three receivers or more quite a bit. So it is easiest for a wide receiver to break out since they have two players who might get hurt and plenty of opportunity to show their stuff while they wait for that to happen. So when I rank wide receivers I look primarily at the player, first their physical talent, and second their experience. Regardless of whatever criteria you choose to use, having a backup draft list is really helpful for several reasons. Secondly, it is a really helpful exercise to do to get to know the league and forming opinions on it.