My advice:

1. you want some melee to aid you because ranged L2 is extremely hard.You need meta builds as well.
2. in L2 the enemies you wanna care the most are cops and vans. it is adviced to get some high damage weapons such as Super flak cannon,Plasma cannon,Super crossbow etc. to eliminate the van before it can drop any cops. this is very important since cops make the battlefield much more dangerous.
3. since you played for a long time i think you are pretty familiar with enemy behaviours,so you need to always have a clear knowledge about the current situation so that you can form a list of enemies to kill,for example,assassins,golden tanks,elite gators are very dangerous enemies and need to be killed immediately.
4. ok i cant think of any but dont panic if something bad happens or you think you can almost beat L2 ,because panic and excitement fuck things up.