It's generally not that difficult to narrow a teams first round pick down to a handful of players.  No matter what "best player available" talk you hear, teams almost always draft for need in the first round.  Combine where your team is drafting with the generally good job done by draft experts on predicting who is considered "first round talent", and you have a good idea of who will be available and worthy of your teams pick.

Lets try that with the Chiefs:

Needs: ROT, C, OLB, NT, WR

Here are five players that play those positions, who will likely be available at pick 21, and arguably have the talent to justify the pick. 

Pretend all players rated higher at these positions have been picked, therefore, you HAVE to pick one of these five.  (Hey its my post, my rules, lol)