I can't find way to change default priority for all tasks I creates. I need this becouse sometimes I want to set priority lower than default.
Tasks are added with the lowest priority already (Priority 4). Do you mean changing it to something higher? Either way, it's not possible to change the default priority for now. Feel free to add it in the votebox https://todoist.com/Vote/.
I agree, this feature is of great importance. Sometimes you have a list with various tasks only to realize that one of them is less important than the rest.
In order to show the difference of importance I had to increase the priority to every single one of the other tasks.
I think the default priority should allow the option for less important tasks.