The word deacon comes from the greek word "diakonos" (1249) which is translated 20 times as minister, 8 times as servant, and 3 times as deacon. BlueLetterBible.org gives the following definitions for deacon:
Let us look at a few verses where "deacon" has been translated as "minister" and "servant", and "deacon":
If any man serve me, let him follow me;
and where I am, there shall also my servant be:
if any man serve me, him will [my] Father honour.
John 12:26
So a deacon is essentially a servant or a minister (which is one who carries out the tasks of another (e.g. satan's ministers II Corinthians 11:4)). In which case, all believers ought to be deacons. In Acts 6:1, we see that several deacons were appointed "because their widows were neglected in the daily ministration (diakonia)". In verse 6, they prayed and laid hands on them, appointing them to the office of a deacon.
From Acts 6:1-7, we can draw several practical conclusions. First, there was a need for someone to "serve tables" (Acts 6:2), or take care of the needs of the widows. Therefore, rather than the elders "leave the word of God" (v.2), they thought it wise to appoint deacons over the business. These deacons served the widows. They were servants.
In summary, all believers are called to be deacons (servants). However, in some cases, depending on the needs of the church, the elders may appoint deacons to handle the business. This should help to free up the elders to continue laboring in the word of God. Also, note that although Paul commanded elders to be appointed (Titus 1:5), he did not command deacons to be appointed.
More specific requirements are found in I Timothy 3:8-13:
Holding the mystery of the faith in a pure conscience.
And let these also first be proved; then let them use the
office of a deacon, being found blameless.
Let the deacons be the husbands of one wife,
For they that have used the office of a deacon well
sober, faithful in all things.
ruling their children and their own houses
well.
purchase to themselves a good degree,
and great boldness in the faith which is in Christ Jesus.
I Timothy 3:8-13
These are all qualities for which all believers should aspire to have, but are required in the case of appointing deacons.