What is the "most important" element must be taken in mind when establish any work team?

Ensure that there is harmony between the members

i would say diversification.

Important is willingness to contribute to team along with harmony between team members. Other things come by default. 

All should have spirit to work as team.

All should be highly skilled.

All should have faith on each other.

All should  be away from dirty office politcs.

Suitability of the selected members to the job(s) in hand.

For building the hi-performing team, a manager or leader must consider the following parameters;

1 – They must be well skilled as per the requirements.

2 – It is not necessary that they would earlier or known to each other, new members must also be part of such team for learning.

3 – They are capable of working in group i.e. team dynamics, eliminate the problem child or brief them in detail for no-negative approach.

4 – To foster creativity, encourage weird ideas and differences of opinion. You may never know that when an idea is clicked out.

5 – Loose temper oriented individual must be danger for such project and too much fun oriented guys are also question mark.

Give them task, establish auto-report for generating feedback and then review the performance against the set target.

I think to amke one thing , Always open channles meaning makeing stuff meeting on weekly basis2 be communicated with your team to know well they work status and they needs as well to reach up the ideal frame work all can work smoothly in it.

Working in Team or Group requires a Mature Understanding and a Balanced Coordination.if your Team grows then your project will Grow And finally your organization will Grow.The Biggest collapse to any kind of relationship is when Understanding dies between people when they are still Alive!!!. A lack of Understanding among them can cause Misunderstanding.The Misunderstanding can not only break Human-relation but can also put Nations at War!. We have to be very strategic and diplomatic  while Establishing any kind of team.But the things wont End here because the biggest challange starts after establishing a Team. It can be overcome by efficiently monitoring them and Rewarding and recognizing their efforts at each and every stage throught the process.

Start with selecting the right people (if it is in your hands)

Chose people with different potentials and abilities.

Chose creative persons

Work out the coordination between them and assign tasks according to their abilities.

Follow up with them

Ensure that the tasks are completed and reported back to the in-charge.

Team Cordination and Attitude of each member in the team.

Positive attitude of each member is a key point in Team work.

Regards

Ragesh Vadakkedath

The only element i know that is very important in establishing a team is "UNITY"

even how smart and genius you are when theres no unity; the team is nothing and will be broken soon!

;)