This depends on your workflow and also depends on where you and your colleague is working.
First and foremost, if you each are working on your own individual branches, there won't be any conflicts to address until you both merge your branches into master, or some other agreed-upon integration branch.
If you're working in the same branch, then the risk of stepping on each other's toes increases, but can be easily mitigated. Git does a decent job already of avoiding silly collisions, but it will happily inform you when there is the potential of a conflict and it will hand back control to you.
If you run into a merge conflict, you and your colleague need to put your heads together to see what caused it, why, and how to mitigate it. Having tests in your code goes a long way to ensure that behavior isn't missing when the conflict is resolved. This is a personnel thing more than a Git thing, as Git can only do so much in that regard.