Benzil's suggestion is a good one.
What I was referring to is that each position has what are called core attributes. This means that certain attributes are more important for certain positions. For example, qb would be GI, Tech and Strength as Core(most important) attributes. There are also secondary but still important attributes that vary dependent on the position . To extend our example of the qb, secondary attributes would be Athleticism(supposedly increases your chances for a big play) and Elusiveness (to keep from being sacked).
Read the GD help files and find the list that details by position the core and secondary attributes. The list also will tell you what you have to practice to raise specific attributes. Not a bad idea to print it out and memorize it or keep it available to refer to.