Fans do generally have a better idea of who their team might pick, mainly because they have a more in depth knowledge of the entire roster and know their team's draft tendancies. Many "so called experts" don't have the time or resources to examine things so in depth for every team. They make player rankings, rank team needs, and then use them to create a mock draft.
In fact it can be very misleading to read such mock drafts because fans will rarely think outside of a certain window of players. For example, many uneducated fans thought that Bobby Carpenter was a second round talent, because many mock drafts had him going in the second round rather than the first, which means nothing in reality. Carpenter was far and away the top SOLB in the draft for the Cowboys defense, yet many publications had him listed as no higher than the 5th best OLB.
My advice to all the draftnicks out there is to skim over these publications to gather names. Once you've done that, focus on players at positions that will likely be drafted.
Don't bother with the 230 lb linebackers and even then don't worry very much about the bigger ones. We just spent two first rounders on OLBs and the rest of the LB corps is very young. On the other hand, take a good look at the top 15-20 WRs next year because our starters are in their 30's, and no one else on the roster has shown the ability to replace them yet.
Once you've narrowed down your list, watch as much college football as possible. Whenever you get a chance, focus in on the players on your list.
As the season progresses, keep the Cowboys' record in mind. Unless we start losing a lot of games, elite players like Calvin Johnson and Adrien Peterson should recieve less of your attention than guys like Ted Ginn and Kenny Irons.