There is a tactic that is commonly used in the world of guerilla warfare: The height advantage.
On levels such as Outskirts, Metropolis and Delta Halo, if you can manage to scale the rooftops or hills, you have the tactical advantage over the enemy. A sniper rifle and another long-range weapon is recommended for this strategy, as you can just poke your head in and out of corners, sniping each enemy patrolling the area. Commonly, the way to get rid of Jackal snipers would be to snipe them in the head from behind. However, it could also be a good idea to sneak up behind them, meleeing them in the back and picking everyone else off in close proximity. Sometimes just a warning shot will cause them to drop their weapon cowardly and try to take you down with just plasma pistols.