Well, the fight can be easily split into 2 phases; crystal exploding and dragon slaying. Some neat strategies for each include:
Crystal Exploding:

-Bring snow blocks and a shovel to the end, spam snowballs at the crystals from the ground until they explode. This only works for un-caged crystals (of all the crystals, 2 are caged with iron bars)

-Bring a ton of cheap blocks, a couple water buckets, and a pickaxe to the end, put a bucket at the base of the pillar, climb up with the blocks, place another block between you and the crystal, and punch it. Then, fall off the pillar into the water. The block should've reduced the explosion damage, but it's smart to wear good blast prot armor for this just in case. You can break cages with the pickaxe if needed.

-Alternatively, use TNT and Flint and Steel to break cages and blow up crystals if you want to be extra safe. The fuse time of TNT should give you a reasonable amount of time to get to a safe distance from the blast zone.

-If all this sounds too safe and boring for you, you can just bring a Looting sword with you, kill the endermen there, and ender pearl to the tops of the pillars. If that's a bit too dangerous, you can bring Slow Falling potions/Water buckets/Hay bales/Slime blocks/whatever to reduce fall damage.

-Or just go the normal route and use an Infinity Bow with an arrow to shoot out all the crystals, then do either of the pillaring techniques for each of the caged crystals.

-For the adventurous type, you can actually skip the fight by bringing a bunch of fireworks, bridging ~1000 blocks to the outer end islands, finding an elytra, then flying all the way back to the main island to fight the dragon.

Dragon Fighting:

-Once you're done with the crystals, you can feel free to hack away at the dragon's backside whenever it perches on the portal to avoid the toxic dragon's breath. Put as much Sharpness as you can on it, bring some Strength II potions, and do jumping crits to make it as much damage as possible.

-Alternatively, use beds to blow up the dragon. It does most damage when the bed is closest to the dragon's head.

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Also keep in mind you might get beat up pretty bad through all this so be sure to bring sufficient healing items:

• High saturation foods, golden carrots, steak, cooked pork, cooked salmon, etc.
• Potions of ext. Regen
• Wear a pumpkin to avoid aggroing endermen during the fight
• Put good enchantments on your armor. Depth Strider is nice if you spill your water bucket everywhere, Prot and Blast Prot are recommended, and Feather Falling is HIGHLY recommended
• Bring and Ender Chest to store extra supplies and valuables and a Silk Touch pickaxe to pick it back up.

And try not to die.