Heres some basic advice to get around the swamp more easily

1) You should expect an ambush when you first enter the biome, particularly if you run around and jump. After this initial wave of monsters the swamp will be calmer provided you do not run around. Walk around slowly and fight monsters 1 or 2 at a time.

2) You should use blunt weapons such as a fully upgraded club or a bronze mace

3) Consider starting with a scouting run where you do not try to fight anything and you do not bring good armor. You can leave all your gear at your base and then use the first boss ability to outrun monsters in the swamp. This way you can know what you are getting into when you explore it for real with your armor.

4) Make a forward base in a black forest or meadow that is close to the swamp

5) Alternatively, look for an abandoned building that is high off the ground in the swamp and make a forward base there, high up from the ground