How do I avoid the error "out of memory"?
There's really not much you can do in this case. Drupal 7 requires fair bit of memory and so do Views, Panels, etc.

If upgrading to a hosting plan where you have at least 128MB is not an option I would at least make sure the following modules are kept disabled:


Update Manager
Database Logging
Field UI
Views UI
Panels In-Place Editor
Any other "UI" module 


Do your development locally and use version control &amp; Features to update your production box.