So, you picked up Dirty Bomb from steam. Good job, welcome to the fold 
Now, you will have noticed this is not your average shooter, you running for your own K/D is not going to be enough. So, I decided to compile some tips for newcomers that may or may not be helpful.
- Run with your melee out and follow the team, seriously. Do it and you will find action.
- Don’t buy a sniper with the credits the game hands you when you begin, you will regret it since everyone moves much faster than you would expect.
- Do your job, simple stuff. Give ammo, heal, revive and do the main objective. Your team will be happy to have you than. Also, equip your defibs as a medic and charge them if you have the time. Everyone likes seeing a full health bar on their team.
- If someone is already planting or defusing C4 as an engineer, defend him and keep him alive. Be a meat shield if you must. It is better to die in overtime and let your engineer defuse the C4/deliver the objective than keeping you K/D high.
- Team up with someone more experienced, they can teach you the game and movement.
- And finally, play the tutorial and the assault course. You will thank me later.