GitHub Desktop + Git LFS / SourceControl issue/tips

So badically me and my small team (3 devs) had setup our GitHub shared repository with Git LFS, we tried to setup Perforce but the server setup doesnt work for us since our routers are kind of complicated to work with opening port and local hosting a server (and we found little to none tutorials about that at the moment). The last time we worked with GitHub Desktop shared repository we had big problems with merging stuff and working on separated aspect of the game, since most of the time on dev work would be overwritten by another dev work. I was wondering if you have some good practices on how to work at the same time on the project without having stuff conflicting (like how to setup maps/project etc.).