I recently had my first victory on insane roguelike and thought I would share what I learned to help others looking to win on higher difficulties do so. There are many small changes to your playstyle that will help bump your survival rate by small degrees, adding them together and you can see your average character death level improve until you eventually win.

Insane difficulty boosts the zone level, creature level and talent level. This means that higher level enemies have higher level abilities, have more health, do more damage, and also spawn much more often than nightmare and normal. This means that sooner or later, you are going to fight a unique or random boss enemy and 3 rares at the same time, it's going to happen. It's probably going to happen a couple of times on insane. Depending on what talents are available to enemies when you are in this situation, you can end up stunned, pinned, confused, all while taking large amounts of damage for successive turns. This can be a very fast game over, and on insane it's a matter of when, not if you get your multiple enemy boss fights.

If you end up running away from this situation with 4 elites, and manage to escape to the level entrance, these 4 elite will be waiting for you with full health when you come back. This ends up in a situation where you are effectively 'locked out' of an area which is fairly bad as you miss the loot and xp. You can go to another zone, but it's 1 less zone with enemies your level you don't have access too, making you take a higher level zone at less experience than you otherwise would be.

To overcome these extreme situations, you need to buy yourself crucial extra turns to let abilities/heals/infusions come off cooldown so you can survive, and kill off an enemy so you don't get 'locked out' of the level. Arguably one of the best abilities in the game for this is a heroism infusion. When I was playing Tome on nightmare, I never took heroism, on insane I always do. If you're really serious about a insane win, I would check the starting shops, and probably start over if there's not a heroism infusion there, it's that important. If you're a purist you'll probably try and make every run work, which is great, but heroism will increase your winning odds by a significant margin.

A technique very useful on insane is using line of sight effectively. On the first level of any hallway zone (Zones that don't have large open areas) use your pickaxe to dig a hallway that makes a square pathway. This allows you to use a movement infusion to back up if things go poorly without accidentally backing up into another unique enemy, which will kill you if it happens.

After you have a large fight with a particularly difficult unique or random boss, back up a few turns before hitting the rest key. Before I started doing this, I would hit rest, then another unique would come into view while all my abilities were still on cooldown. This can and will save your life playing on insane.

Don't underestimate rare level enemies. The skill and level bonus they get on insane mean they are deadly, much like the emperor, your overconfidence is your weakness. Think of your standard starting nuke as an interview with your enemy elite. You should have a feel for your opening damage should take off about 1/4 the enemies health, if it doesn't, consider this interview going very poorly and pay attention or end up dead.

Have a basic understanding of enemy loadouts. There are tons of great classes in Tome, uniques and rares will usually have a base class loadout (sometimes they can have skills for multiple classes which can be pretty scary also). Knowing what they want to do and avoiding it will help you avoid realizing that this rare hit me for half my health in 1 turn before it's too late. For example: anything with a melee weapon wants to close the distance, so avoid rush range, don't let a brawler grapple you-ever! kill the slimes of oozemancers, ect. One personal motto here-if a rare or higher level enemy is wielding steamguns, treat the game like it could be over next turn and play accordingly. Steamgunners with strafe have extreme damage output and very high critical rate, the shot also has a unique sound which nearly gives me PTSD. Always be very careful with steamgun enemies!

Itemize appropriately. Until you get to at least lvl 20, treat any gear with +30-40 health as a best in slot item, period. Check starting shops and buy any item you can use that has +health on it. It does not matter if you're playing a Solipsist with 90% damage is mind damage and you find a pickaxe that gives +20%mind damage, until you get skill that provide additional  healing, status resist, or escape, your chance of dying far outweighs your damage output. Early game on insane is about surviving enemy damage spikes and debuffs while steadily wearing down enemies until you win. Once you have more survival talents and a prodigy you can look at increasing damage output and status resist, but early on +hp gear is the best you can get.

Have a zone order and know you class strengths and weakness. Open zones that don't have narrow corridors I consider generally safer than hallway/large room zones. This is because on insane, large room areas tend to have a concentration of enemies, which will end up leading to fights with multiple rares/uniques. Also if you go down one hallway off a large room and end up running away from a deadly boss, another rare/ unique can come from another hallway, attracted from the noise of battle. That being said, some classes with beam spells excel at having enemies lined up like an archmage, while other like a summoner are terrible in this situation as you want multiple summons hitting the enemies every turn and in a hallway only 2 can. Because of the dangers of hallway and large room loadouts, I would strongly recommend leaving the gloom and norgos lair for the last 2 tier 1 zones. If I haven't found much +hp gear I skip them completely and suggest the same.

Know when enough is enough. Sometimes you will run into a unique or random boss that you cannot kill or whose damage output is extremely high. When this happens you have to kind of swallow your pride and just leave it alone, it's not worth a game over. I recall on my insane winner running into a unique paradox mage in Daikara that had time shield and a torque that healed him for almost his entire health pool. I ended up leaving him there until I came back 10 levels latter. These strong enemies do leave you 'locked out' of a zone, but you have to weigh the risk. Bad luck can happen where you end up locked out of multiple zones, this can lead to a game over just because you have to go to a higher zone level too early so try and avoid this also, it's a balancing act, just requires practice to get the feel of it.