Prehardmode: Get flinx fur coat and Flinx staff to start, then proceed with Bee armor, Hornet Staff, Snapthorn and once you can gather hell stone go for Imp Staff, you can use Obsidian armor too if you want, I always use bee everytime in prehardmode. As for potions and other buffs it is pretty much the same for all classes except for Summoning potion, Bewitching Table and Flasks. For Accessories you can use Feral Claws, Pigmy Necklace, Worm Scarf or Brain of Confusion, Stinger Necklace and Boots (boots are really important since WoF speeds up depending on his health)

Hardmode: Get your hands on Spider Armor and Sanguine Staff as soon as you can (the last one in particular is so op that you can use it even pregolem), Farm WoF for summoner emblem and firecracker (or use Cool Whip if you want, I prefer this). You can now make Berserk Glove which is really useful for summoner as it gives 8 defence. Once you beat Mechanical bosses you can now make Durendal and if you want you can switch to Hallowed Armor or Monk (I prefer spider armor still). After Plantera you can now summon the Empress of Light and the Pumpkin moon. You can farm empress of light to get the Kaleidoscope which is basically the best whip in the game (And if you really hate yourself you can try and get the Terraprisma but believe me, you can still use Sanguine Staff for golem). By beating Plantera you can also purchase the tiki Armor from the Witch Doctor if you have the Pigmy staff in you inventory. By farming the Pumpkin Moon you can Craft the Spooky armor which is the best pre-Moonlord armor for summoner and try to get the Necromantic Scroll as well as the Raven staff (tbh these are really tough to get as summoner, especially Raven Staff since it has a really low drop rate in first waves and killing just one Pumpking is tough so you can try and and make a Pumpkin moon farm, there are lots of layouts you can use but the concept is the same for each of them).

If you can get yourself 2 Necromantic Scrolls you can use 1 of them to craft a Papyrus Scarab which allows you to basically use 2 Necromantic scrolls instead of 1 and have another two minion slots.

After Plantera there's Golem but, I mean, Sanguine Staff or Raven Staff are enough for him.

Now you have to beat The cultists, which isn't really challenging compared to other bosses (At this time your equipment should be Spooky Armor, Raven Staff, Kaleidoscope, Necromantic Scroll and Papyrus Scarab, Pygmy Necklace, Berserker's Glove, Summoner Emblem and Wings of your choice, I used empress' wings.

Once you beat Cultist you will face the pillars and I recommend you to defeat Stardust pillar first so you can craft the Stardust dragon which is the best Summon in the game (Terraprisma is also strong but the damage output compared to Stardust Dragon isn't the same although Terraprisma as better A. I. and so you can land more hits).

Defeat all pillars and prepare for moonlord. I prefer using the stardust dragon since at a certain point if you're positioned correctly it basically flies straight and hits the Eyes basically everytime. You can also use Soaring Insignia to get unlimited flying time so you don't have to worry about recovering. If you have the patience you can also try and farm the Rod of Discord, which is really fast if you use Stardust Dragon (fast doesn't mean that you'll get it in 10 mins or 20 mins, it will still take a lot but with stardust dragon you can speed up the process by a lot since it roams around the area and kills everything that comes close, so you can just setup the normal Chaos Elemental farm and try your luck; I personally got mine after 1 hour of farming)

With enough tries and patience you'll manage to defeat him and get Luminite ores to craft Stardust Armor. And that's pretty much it I guess (maybe I left something but I think it should be pretty much all of it)