Many people recommend that teams should be diverse, but… In a way, this goes against human nature. A clear stage in psychological development is identifying with a particular group. That is where one feels secure. Conversely, one tends to be sceptical of other groups. 

Many teams have more or less "cloned" members. It's not good, but diversity is harder to work well. Are there any tips?

One tip is to strive for everyone in the team to be a world champion at something, i.e. the best in the team at something that the team needs from time to time. Then that member will feel in demand and thus important. This, in turn, makes you inclined to be humble about the competence of others in the team. In addition, if you have a common goal, which everyone has understood and accepted, then you have a good basis for countering destructive conflicts. Healthy conflicts always exist. The trick is to manage the conflicts in a balanced way related to everyone's needs.