Make sure you start each mission with at least 750 of each resource and 75% of the maximum of any ammunition you will use. Make sure your weapons have at least 50% durability remaining, or a replacement ready to go.
Communication is vital to completing difficult missions, and it makes the game a lot more fun. At the very least, when starting a match, let your teammates know which role you will be playing, and watch the game chat for status messages from others. If possible, listen in to what people are saying on comms, and speak up if you have a mic.
There are 4 primary roles to every mission: builder, gatherer, defender, and explorer. While these roles quite naturally fit the 4 main classes in Fortnite, it is not required for the builder to be a Constructor or the gatherer to be an Outlander. In addition, not every mission will break down evenly to one person per role, and several players may share and swap roles throughout a mission. However, maximum efficiency can be achieved when all 4 roles are filled.
The builder is responsible for placing the initial fort layout. This skeleton will include level 1 floors, walls, ramps and stairs in the appropriate material. The builder will analyze the terrain and place appropriate chokepoints.
The gatherer is responsible for collecting resources and bringing them back to the builder and others who are upgrading the fort.
The defender is responsible for protecting the builder from random husks. Depending on the mission, this may not be a full-time job, and the defender can help gather resources near the objective site.
The explorer is responsible for rescuing survivors, collecting Blu Glo and destroying enemy encampments.