@natalia_skoczylas we have been taught that a consortium has a lot more chances if it is embedded in the topic. That normally means, at a minimum, being led by a high prestige org which has won projects under the same call (TRANSFORMATIONS) before.
In practice, this type of org tends to have a consortium already lined up. So, in the two successful proposals of 2018, we joined existing consortia rather than making our own. This is easier and tends to be more successful. The price we paid was that we could propose other partners, but in some cases the leading organisation said no: they had their own agenda and partners.
If you follow this strategy too, my advice would be not to make promises to third parties until you have a deal in place with the consortium leader, and to leave space in the consortium for key partners, especially the leader. @anique.yael can tell you much more about this.