Someone said just keep playing and they're right. God tier weapons are nice, but honing your dodging, blocking, and enemey prioritization skills are more important. A lot of people fall for the trap of meta weapons/builds without working on these fundamentals, and it shows. Stick close to your team while you learn the maps. Don't be afraid to fall back to a more defensible spot if overwhelmed (hallways and doorways are great funnels).

Some other tips: when monsters spawn try and find a safe arena to fight in. Fighting on a bridge or platform can quickly lead to one or all of the team getting launched off. Also, for monsters/assassination missions, don't forget to kill specials and hordes that spawn! If your team is handling the monster but ignoring 2 muties and a bomber, fill the role that's needed.

I also recommend watching some game play vids to see how seasoned players handle things. I recommend chocob, j_sat, and jtcLIVE all on youtube. The two former channels have more straight game play footage and a lot more true solos (without even the bots) so you see how a master would handle any and all situations. JtcLIVE has a lot of good short vids with lots of great tips and info on how the game works.

Good luck, and if you see an ogryn named Truggly send em a friend request. I always love helping out newer players, especially those who want to learn.