Welcome to the game.
First off the bat make sure you grab Zortargs game guide found here under guides.
I too play Green Pellistal whoo hoo.
There are 13 tiers in the game currently. To keep it simple for a new player lets talk only about T1 T2 T3 and T4.
T1 is basic T2 has same stats but lighter, T3 better stats but heavier and finally T4 one of the best in game heavier and harder to fit with extensions. So that is the gear side of things. Also you can raise the weapons skills. On top of that for missiles the key is the seismics skill, basically means more of your missile damage explodes on top of the enemy.
You can increase your missile cycle time using extensions so you shoot faster. You can increase the missiles range to shoot further. Also you can put some gear on top of your head for each specific weapon type to increase DPS.
So look for missiles weapons tuning s on the marketplace.
Keep in mind there are 2 sizes of missiles small and medium.
Each robot in game has a different size, smaller robots are harder to hit and also well smaller.
You can find each robot size in the information panel in game.
Medium sized missiles do more damage but the explosion size is so much larger you actually do less total damage against smaller robots. This can be reduced with seismics skill and the leg modules weapon stabilizer modules.
Hope that helps you out, good choice on the robots.
Edited 1 time because Jita was more accurate then first reply.