With the draft one week away, the Cowboys' front office is setting up its draft board. Contrary to what many fans believe, the Cowboys don't rank their board vertically (just a ranking of prospects regardless of position) but actually horizontally (players are ranked in tiers, by position) as evidence by their leaked draft board from the 2013 NFL draft.
This approach means the Cowboys don't select the best player available, but actually the best grade available. A player's grade takes into account how good a player is, their medical background, their character and if they play a position of need. For example, a prospect that plays at weak- or strong-side defensive end would get a bump in their grade.
This is why it is unlikely the Cowboys draft a player like Johnny Manziel in the first round. While Manziel may be ranked higher on a "vertical" board than a player like Zack Martin, Martin will likely have a higher grade for the Cowboys specifically because he addresses a position of need.
Blogging the Boys' Joey Ickes gave a great explanation of the Cowboys' horizontal draft board:
How that player fills a need might bump a guy from a 1.15 (middle of first round), up to a 1.13 ( Top 1/3 of the first round) grade, where as failing to fit the scheme, or play a premium position might drop a guy from a 1.12 (Top 5 player in round 1) down to a 1.18 or 1.22 type grade (where Shariff Floyd likely should have fallen on the Cowboys board in 2013). So taking the player with the highest grade available means that before the draft, when you are not in the heat of the moment, you have taken things like your self evaluation of your team, your projection of the prospects' talent, their fit in your schemes, whether they are the RKG, their medical condition and any other information you obtain into account in your slotting of those players. Then when you get to your pick in the draft, you've already got guys in position where you feel comfortable taking them, and it's not based on some partial evaluation or short sighted criteria, like the best talent available or a pure team need.
Therefore, players from a position of need will likely get a bump. Now you might be thinking, "Which positions are needs for the Cowboys?"
I'm glad you asked.
The criteria I used was an assessment of which positions are the weakest on the team, how big of a negative impact it will have if that position is not filled and how important that position is on the team.