The importance of team building is difficult to overestimate. The human factor remains king no matter what sphere we are talking about. The ability to form an effective team is probably one of the most important key competences of a successful project manager.
While considering who to choose, remember that the set of skills brought by each member should be able to add some extra value to the team as a whole.
Every project has their own requirements and roles are chosen accordingly depending on one’s ranks, experience, skill, knowledge etc. Consider these steps while choosing the right mix of individuals to create an efficient team for any project.

Identify the objectives: Knowing the objectives one can decide on the type of demographics you can choose from. Task parameters decide the type of skills and capabilities required to accomplish the project successfully.
Select team members: From a pool of eligible team members one needs to shortlist those who have the needed task and team-specific competencies. To build an effective team, you must focus on both skills that a team member needs to possess and the pool of skills the entire team needs to have.
Optimize the performance of the team: Just building a team and delegating tasks to members is not enough. One needs to calibrate the performance of the team members and keep reminding them that they need to work as one team to achieve the goal that is pre-designed.
Keep the team going out of the workplace: In order to bring more value, you should interact with each other out of the office. There are lots of team-building events which can be held to make the relationships stronger. Thus, the whole team learns to understand each other and as a result, work in a more productive way.
As a project manager, you’ve got a unique opportunity to help your team be the best it can be.