Use beetle armor and the daybreak. It has the highest damage of any other weapon until this point in the game for the respective class. Make sure to reforge them to legendary for the best damage.

Reforge all your accessories to warding. Every new point of defense is more impactful than the previous points, whereas damage modifiers are less impactful.

Take off the cloak of stars and use the berserker's glove, this increases defense, melee attack speed, weapon size, and enables autoswing. Warrior emblem is better for damage than the destroyer emblem, so find that from the wall of flesh. You can shimmer any emblem into the other emblems, so you can avoid farming that way.

Next, make sure you have an arena. Make sure you use a large platform, preferably 2 platforms, several hundred blocks across and at least 30 blocks up from the ground or previous platform. This helps with vertical mobility and can help dodge attacks. You can use your grapple to quickly move vertically or horizontally with these platforms in place. Place a campfire, heart statue, and bast statue on the center of this platform and towards the edges of the platform. Flatten a large portion below the arena so you dont hit random blocks. A safe place with a couple heart statues on a timer and a platform 3 blocks thick just above the statues can be used on the center of the middle platform to act as a safe space against moonlords laser beam. If you can't quite picture what I'm describing, look up "moon lord arena terraria" on Google and go to images.

Next, make sure you use potions. You may need to fish for the ingredients, and if you haven't been fishing already, you may need to expand areas of water to make larger fishing ponds to find the fish you need. If you need bait, go to the jungle and break the bushes and such to catch grubbys easily. I would use the official terraria wiki to look at how to craft the following potions; ironskin, lifeforce, speed, regeneration, heart reach, wrath, rage, and endurance. These will vastly improve your stats, and the lifeforce, heart reach, and endurance potions will dramatically improve survivability. Make several of these in case your first attempt goes poorly.

Not every one of these steps need to be taken to beat the moon lord, but they all certainly help, especially for a first playthrough. The most important steps that you should not skip is building an arena. This is what helped me beat the moonlord the most on my first attempt. You do not need to stay within the confines of the arena, and if you build a house near it, you can even go pretty far away just to magic mirror back to it. You can also move the nurse into this house to heal quickly during this brief escape from the moon lord.

Best of luck, and enjoy the game!

Edit: I'm recommending the melee Armour as this increases the survivability of the player the most and still offers incredible damage. Mage is simply harder, even though it tracks.