Git Branching - Best Practices - Large project - long running branches

Hello, I work on a team of 15+ developers. We are trying to determine best practices for branching because we have had code stepped on when a developer has a long running feature branch.

We have a Development branch. Developers are instructed to create a branch when they begin working on a feature. Sometimes a feature may take a week or two to complete. So a Developer1 creates a branch and works for a week or two. In the meantime, other developers have created feature branches from Development and merged them back into Development. 

At this point we are not certain if Developer1 should: 
* Periodically merge the evolving Origin/Development into their Feature branch and when they are done work merge their feature branch into Origin/Development. 

OR 

* Stay on their pure feature branch and when they are done merge into Origin/Development. 

We have had issues with developers stepping on code when they have long running branches. We are looking for a best practices. 

Thank you, Joe Mayne