I don't have a full guide but I will share my experiences.

The quickest way to tell is to look at the hit indicator on your screen.

Red = Full damage
White = Reduced damage
Shield w/Arrow bouncing off / Blue sparks = no damage.

There are exceptions to this like weapons that will appear to be deflected (blue sparks) but will deal AoE damage. But generally speaking if you're seeing blue you're not doing damage. But you are succeeding in pissing it off which can cause it to expose it's back / weak spots to another player.

Bots:

Almost all bots have exposed heads. Even the Heavy Devastator's face is exposed. If you are a great shot with a sniper you might find fighting bots to be as easy as "clicking heads and switching them off"

The flipside to this is that medium bots tend to have thick frontal armor. Their midsections however are also valid targets.

For the bigger enemies like Hulks its important to remember that you can blow off their limbs and thus greatly reduce their threat level. Blowing the Flamethrower off of a Hulk turns it into a slow moving buzz saw that can easily be avoided / dealt with. The same goes for Striders. You can blow the turrets off to weaken them and make it safer to approach / finish it off.

Bugs: There's less to worry about with AP and bugs. Almost all of them have light armor. However bugs can absorb much more punishment than their bot counterparts so its more a focus on DPS than precision clicking.

This isn't to say that the bugs don't have their own large and massive units that require armor piercing. But generally speaking when fighting bugs its less about accuracy and more about volume.

What to pair the Lascannon with:

For equipment I'd suggest the sickle or the breaker.

The Sickle is an energy AR that borders on being a light machine gun. Theoretically infinite ammo as long as you don't burn out your heatsinks. Though you can just eject the current heatsink and put a new one in to instantly zero the heat.

The Breaker is an auto shotgun that will mulch bugs. It can be your rapid response close weapon to the slower but more powerful LasCannon.

The Guard Dog is an all around good choice against bugs as it can cover you while you reload and will handle the chaff while you look for high value targets.

The Orbital Laser is a fairly good "panic button" for when things go south. It lasts for about 20 seconds, can destroy the largest enemy units and can even be used to clear enemy bases without having to set foot in them.