The current trend in coach and player education is to refer to positions based on the numbering system the English FA (Football Association) made mandatory in the late 1920s. The system began by numbering the Goalkeeper as #1, followed by the 10 outfield players being numbered sequentially in a 2-3-5 formation.
The Right Defender and Left Defender are numbered #2 and #3 respectively. The Midfield Three come next as: Right Midfielder #4, Central Midfielder #5 and Left Midfielder #6. Finally, the five Forwards are labeled (from left to right), the Right Wing as #7, Inside Right Forward as #8, Central Forward as #9, Inside Left Forward as #10 and the Left Wing as #11.
I find it easier to see the right sided players on the right and vice versa, so I draw my teams as moving up the field on a team sheet (above). If you do the same, you just have to number your players from right to left.
Just before jersey numbering was introduced, the Offside Law was altered to become less restrictive. The move was an effort to increase scoring. In 1924/25, 4,700 goals were scored in England's professional leagues. The 1925/26 season was the first under the new law and saw an increase to more than 6,300 goals. The change however led to the creation of safer and safer formations.
The first player to move back to the Defensive Line, was the Central Midfielder #5. Eventually the #4 followed. This is why English Commentators (still) refer to Central Defenders as Center Halfs.
Over the years, it became inefficient to keep five Forwards so the #8 and #10 were moved back. Typically nowadays, the #6 is considered a Defensive Central Midfielder, the #8 is often referred to as a "Box-to-Box Midfielder (being expected to cover the ground between one penalty box and the other), and the #10 is still regarded as an Attacking Central Mid or "Playmaker."
The #7 and #11 were the most wide of Forwards and still today are described as "Wingers." They play in the flanks on the right and left respectively. The #9 has always stayed high up the field and central. That said, a position that was once defined by the tall / strong workhorse is now just as often played by small / quick / skillful / creative players.
The picture below diagrams a typical set up for the 2015 and 2016 Cardinal Teams. You're going to want to understand the difference between a #6 and a #8 9and all numbers) as in the Fall, we'll be telling people to play the #7 role (for example) instead of telling you to play as a Right Wing.