A couple of tips:
Fighters and knights have a shield and an armor slot, so they can go right up against weak monsters and expect to take no damage. They have horrible range, but that can be fixed by getting a mythril sword; which triples your attack range.
Anyone with a magic slot (Priests, Wizards, Paladins) can equip both attack and healing spells. Priests/Wizards can't wear armor, so their defense is crap. Obtaining a ring (or two) of defense/greater defense should be a priority.
Monsters do not spawn on beaches, but they can still shoot and be lured there.
Use your minimap to find other players. They're the green dots. Zoom out (-/+) to keep track of players that are farther away.
TRAVEL IN GROUPS.
1. If you hit the monster at least once and someone else kills it, you still get experience.
2. Every person with a heal spell improves your survivability massively.
3. Every bullet they take is a bullet you don't.
4. Heal spells affect everyone on the caster's screen, so spreading damage around makes their healing more cost-efficient.
5. If you do die, they can salvage your equipment and maybe even bring it back to you.
6. Unless you stay near the beaches, you're going to be swarmed on all sides.