Conceal Shot 2 (Source)

Concealment chance: Different mobs have different behavior patterns. When you /examine a MOB you can see if they are pack, herd, aggressive, stalker etc. If you are attacking a MOB that is aggressive or packing, expect it's friends to attack when it is attacked due to it's "pack" disposition. If you have higher concealment chance, you have higher odds of being able to begin attacking 1 of these types of mobs without drawing its friends into the battle.

Pulling: Pulling is a technique for pulling 1 aggressive/packing mob away from a group without drawing aggro from others nearby. There are entire FAQ's on how to do this, but the easiest for a riflemen is as follows. Get to your ideal range, go prone (/takecover does not help - explain that in a minute) and hit a mindshot on the mob you wish to pull. Immediately peace. Back up to about 90 meters and wait for the bleed to tick. As soon as the bleed ticks you will be engaged with the mob. All others will remain in place.

/takecover: Take cover adds to a riflemen's ranged defenses. You can take cover from prone and ranged enemies will have a harder time hitting you. This comes in handy if you are running faction missions, attacking Nym's guards, marauders, or other gun-wielding NPC's. It has no other benefits and is rarely used by most riflemen - many of us wish for this to give us more of a benefit.

Conceal shot: Conceal shot works endlessly as long as you never draw a random bleed and never miss more than 1 time in a row. It is beneficial, but not necessary to use /aim before each concealshot in order to increase your chances of hitting and not missing. The time it takes to aim before each conceal shot on a large mob will double the time it takes to kill the mob - not worth it to most. Example: takes 45 minutes to kill a giant canyon krayt dragon with conceal shot without aiming and 1 1/2 hours with aiming. It is faster to keep a speeder close by and a pet on guard than to aim between each shot.

PVP: Prone, conceal, and take cover are not viable in PVP. Unfortunately riflemen are heavy machine gunners in this game and not snipers. If you are laying on the ground, trying to be sneaky in any way, you're dead. Riflemen's place in pvp is in the back, using flushing to reduce large #'s of enemies defenses as fast as possible and then draining their minds with headshots.