Before you start trying to solo missions or go for high tier loot, I suggest you grind some lower tier missions until you get good at dodging and other game mechanics.

Get to know the missions you will encounter. A good way is to keep checking the chat (Bottom Left Corner of your screen) to see what missions are being run/hosted by more experienced players.

Practise dodging the mobs and get used to their movement patterns. Running a mission until you can do it casually is good practise for increasing proficiency. For Example, The Hopper Queen The Fire Forest Midboss is good for practising dodging since it shoots many projectiles, same with the Midboss in Frozen Blight.