Mass Effect 3: Surviving Insanity Difficulty Mode
No More Running and Gunning
Your cowboy days are over. If you plan on standing in the open and blasting opponents, you'll soon find Shepard corpsified.
You're going to have to start treating Mass Effect 3 like the cover shooter it is. You're going to have to be careful when you stick your head out, and you'll have to learn to keep your distance. There are a lot of melee units in ME3, and in Insanity mode, they'll swarm you like locusts.
Equipment and Weight Management
You're going to need any edge you can get on Insanity mode. And one of the biggest assets you have--and one that rookies often overlook--is equipment. Upgrading your armor can give you massive bonuses to damage and defense; upgrading your guns can turn a gun that kills in three shots to a gun that can kill with one at a relatively inexpensive cost.
There's also the matter of weight. Your guns all weigh something, and the more weight you carry, the slower your skill recharge weight. For classes that are particularly dependent on skills, such as a biotic, you may want to carry a minimum of equipment. At the least you should opt for lighter guns, even if they do less damage. Its a delicate balance, and changing it costs nothing, so experiment.
Don't let sentimentality effect who you bring with you on a mission. You need to pick the squad that fits the mission. If you're going up against geth, for example, you'll need to pick a squad with strong anti-AI skills. For a mission with lots of melee enemies, think about bringing along someone who can deal with swarms--like a biotic--and someone that can handle up close brawling--like a Krogan.