It's hard at first and it happens to all of us but you just got to keep at it. My first Dunes party really sucked but the next one was great. Look for a few things when you join a party: maximum of 2 level gap, the leader is above rank 4, party has white mage or experienced other mage, and the tank is not a subless warrior. Also make sure you are using an axe or great axe, because although swords at the level for warrior aren't much of a difference, it will show other members that you understand your job's strengths. Good luck!