If you want to better yourself in Enter the Gungeon, I suggest that you start small and listen to the small tips a man can give you in a game that he's suffered for more than a hundred hours.
Other ETG Guides:
Dodge Rolling and It's Appropriate Use
If I were to give you some tips about how not to get hit, my first tip is to not rely on dodge rolling too much during the game. Moving carefully to the left, right, or up and down is just enough against low-risk enemies like the bullet kin, shotgun kin, sniper bullets, etc. Even though Dodge rolling is really important to the game's raw core, it's also important to know when to use it. Evading bullets should be an easy task when it comes to small enemies and should never make you feel like you're fighting a harder enemy.
A good place to start is to memorize the different attack patterns of enemies in an area. You know that the Apprentice Gunjurer fires a large amount of bullets to where you will be, so you don't have to dodge roll it because you can move in the opposite direction once the bullets are fired. Trickier enemies such as the Lead Maiden and Revolvenant require a little more attention, causing you to be painted in to a corner (especially if they are other enemies in the room) it's better to dodge roll in that situation to move away from their line of fire or spread and get a clean kill from there.
Any enemy that fires their weapon according to where you will be can easily be avoided by moving in the opposite direction (As stated earlier) With enemies like the Veteran Shot gun, to the Gun cultist, and such range from a bullet spread and one singular bullet that will hit you. Best thing to do is to be unsure of where you want to move when encountering these foes. Move left, right, up, down, sideways, upside-down to avoid getting hit. If you find this method to be confusing you can also dodge roll into the bullets to evade them, getting you closer to your enemy and deleting them with your gun or Casey.
Any enemy that shoots bullets that spread over time is best to be dodge rolled. When facing a Muzzle Wisp, Poopulon, Creech, Shotgrub, etc. it is better to dodge roll away from the incoming bullets and get the bullet hell away from them (heh). If you can't dodge roll to the sides of the spread of bullets, go straight through it to better avoid taking a hit. Mutant Shotgun kin are faster than usual, and when dodge rolling through their bullets, try a sideways roll (they're a little too fast to tackle head on).
Floor 1 - 5 Bosses
Don't let these baddies get to you. You are a novice now and it's okay to get hit when fighting a giant scary thing with guns that will kill you.
A little tip here is to know your enemy, before you can even fire your B grade weapon, you have to learn a boss' weakness. Which is just an onslaught of your own bullets. After you learn a boss' attack patterns you are free to kick 'em where it hurts! (unless it's Gorgun). But wait! - you still have to avoid their bullets, hooray! Try your best to avoid every single bullet thrown at you, and the best way to practice is the Boss Rush mode. This mode throws you into every main boss you can encounter (not secret chamber bosses). With the one downside of facing each ball of cancer, you don't have to encounter a whole floor just to get to them. So now you have all your attention on the bosses.
Though I've never completed the boss rush (Only to Wallmonger) I still know to remember how to avoid a barrage of red death dots floating to my direction. With the first floor bosses you're already introduced to the fact that you have to dodge roll each bullet (But if you're a decent player such as myself you can half ♥♥♥ it), If you know your dodge rolling skills well enough, you won't get hit by any bullets and you're safe to collect No Masuta Enkei (The master round).
Now it's floor two. You're pressured to use your blanks more often then not. When Facing The Beholster, go for the gaps between his bullet spread where the smaller gun isn't being fired to avoid a hit. During Ammoconda's stupid cancerous existence, you can nope his little blobs of Spaz giving and try your best avoid his attack patterns that the Easter Bunny coloured him in a hundred layers of different paints. Gorgun's fine, just avoid her lame banshee phase and you'll do fine.
Floor three bosses depend on you having kickass loot and good to great dodge rolling capabilities. If you have ♥♥♥ weapons and your good ones ran out of ammo, good for you, you can't progress normally anymore. Cannonblarg's shadow phase is the hard part, so if you dodge all of that you're good to go. If Treadnaught doesn't magically assault you with his wide arsenal of attacks that say "Ha, you got hit noob" on the rounds, you're a god. Finally, if you have walls to protect you from the Mine Flayer, it's smooth sailing. If there aren't any walls, keep your chin up and kill that thing with your Yari Launcher. An actual note here, don't panic whenever facing these bosses up until now. If things seem to get rough, play some calm music or pause the game a little more often to wind down.
Floor four hates your existence more than you hate their's, if those bosses get one hit on you, you start to die inside by 0.0023%. The Statues are the easiest of the three because of their predictable attack patterns. Try your best not get hit by their spinning jammed bullets by dodge rolling more often. When they're bouncing around, get far away from them so you can predict where their bullets are going. The High Priest has some tricky shots. Avoid his fast bullet that can home onto you and dodge roll the heck out of the bullets coming from walls phase. Wallmonger is your Ammoconda that spat out a worse cancer than before, the only thing I can say is to buy a lot of blanks and avoid being hit by his fire and don't move to much when he's firing his walls of bullets.
When fighting the Dragun, be the best you you can be. Go Sicko Mode on this being of shells and show him no mercy when he's spewing out his attacks like how a little obese kid eats at a Golden Corral. There's no guarantee that you will get a master round here, but if you got previous ones you can have enough health to beat this abomination into the lava.
Secret Floors and Bosses
This will help you find secret floors and how to destroy the bosses in them.
Oubliette: To reach this area you must douse the flame in a fireplace with a sacred water barrel (any old barrel of H2O) in the first chamber. You the unlock a room that you must then unlock a trapdoor with two locks on it. Alright, now that you've defeated every room prior, it's time for you to face the Blobulord. The red blob with no soul and a deadly blow to match. A tip here is to dodge roll away from his beam of balls and to avoid everything else by moving slightly If you dodge roll during his squirts of randomly floating bullets is rather to go further away from him. If you dodge roll during this stage, you may get hit by a surprise bullet. Everything else is a cake walk to master about him.
Abbey of the True Gun: To get to this floor, all you need is the crest from the Oubliette. one catch, you can't get hit until you reach the place with the tombstones. A while after you've completed a mildly creepy floor, you can now face the old king himself, the Old King... For starters, this boss is already harder than the blob of red ♥♥♥ known as the Blobulord and is much more powerful than the Bullet King. His jammed bullets fly faster than the rest, so dodge roll towards them to make sure that you don't hit any when dodge rolling to the sides. Some bullets he exerts returns to him, while this happens, shoot from afar and avoid this phase. When firing his circle shaped bullets, run away from them until they disappear. I hope that you don't get hit, but enjoy yourself. Though... you can skip all of his ♥♥♥ if you kill his Chancellor with the Casey, it will one shot the Old King (So he can game end himself).
The Resourceful Rat's lair: To get here you must get the rat key from the second Chamber with lots of moneys. In the third Chamber you need to find a trapdoor and fall into it. Get into a mine cart and go all the way to the end of the large room and use a blank to open a wall, then get to the end of that small area and blank again. when Approaching your small tactical friend, always be on alert. His attack patterns roll onto you like thousands of needles being poked into your soul. Try your best to avoid his kunais by dodge rolling towards them. Be careful for his mouse traps during this whole phase, and rest of the attacks seem to be fun to dodge. In his second phase, he's gonna do anything to kill you. Whenever he does the laser attack, move to the corner of the screen (I tried, it works). Whenever he does the sniper scope attack, make sure that most of those bullets hit the wall. During other attacks, feel free to blank and dodge the heck out of it.
R&G Department: In the fourth floor, you can access a sewer grid with the Sewer Creep in it. If you give him one master round and two items (any kind, rarity... trash is good) and he'll let you inside. After you've completed this really cool area, you must now face Agunim (played by Cam Clarke). Agunim is sheer super-cancer compared to Ammoconda and Wallmonger. Dodge everything, be careful of his fire attacks and avoid those big blobs of Hemorrhoids at you. This guy is really hard, so avoiding this whole floor is probably a good idea.
Whenever you feel stressed about playing this game, I'm sorry that you find real life value in it. Getting mad at a hit is relatable and will always happen, it's important to know how to deal with that anger too. A place to start is to not listen to the in-game music too often, some people find it too hype up when facing a smaller enemy. Try to make your own music playlist that you know will help you conquer this game (this strategy works really well with boosting morale).
If you ever feel overwhelmed with all the events happening during the game, it's okay to pause it and take a sip of your G-fuel. Enter the Gungeon is meant to be a hard and invested game, everything wants you dead and if you ever die to the Dragun with 2 life left you'd probably want yourself dead too. The thing is to remember to keep calm and fire on my friend.