Cheat: Easy XP
1) At the start of the game, you can hunt in the forest to gain XP.
2) Go to the multiplayer menu and set up a private match. Choose the Beach map while selecting Rescue Mode. Choose the Survivor Team and select customise Loadouts. Select the option at the top and choose 'Second Wind' as the Offensive skill.
Set the Survival skill set to 'Advanced Looting'. Now go to Match Options and change the Time Limit. You can choose anything here but 10 minutes is recommended. Set 'Medktis to retrieve' option to 20. Begin the game and run around the map collecting the medkits as quickly as possible and return them to the drop-off point. Collect salvage along the way. You can now keep repeating the match and earning XP and salvage at a rapid rate. It's estimated that this will bring in around 10,000 XP and 2,000 salvage every five minutes.