I should mention there exists a document that provides better HR1-4 sets than described in here, but they are not at all required to beat the quests. If you struggle or want to optimize a bit more feel free to check it out.
In these early ranks, it is easy to feel overwhelmed by the sheer amount of unexplained mechanics. For this reason I heavily recommend to consider following the Leap's progression Guide. It will explained all important mechanics and also give recommendations for armor sets and weapons. But basically equipment wise get the rathalos armor from your welcome pack and a resolute weapon and you should fly through HR1.
At HR2 you get access to Rukodiora, an elder dragon exclusive to Frontier. His armor is very strong and easy to make so this will be your best bet and should carry you through all the ranks up to HR5.
These ranks should not be difficult to get through with your current armor and weapon, so nothing special here. At HR4 however you can unlock the Silver Hypnoc SnS by following the Hunter Navi. It is not strictly better than the resolute weapon but maybe you appreciate a change at this point.
At this rank you finally get access to the two new hunting styles Heaven and Storm. Generally speaking SnS prefers the Storm Style but both are perfectly fine to use. For a more in depth explanation check the playstyle section.
You will also notice that the monsters are getting tougher and your current set will not be enough anymore. Don't worry though, HR5 and especially HR6 are viewed as the biggest spike in difficulty in the game and struggle is expected. There are two sets I would recommend you build at this point, the first you can craft at HR5. This can be good enough to get you through HR6 too, but if you still struggle be sure to make the second set craftable at HR6 too.
As for weapons note that SnS shines with element. Especially if you play storm style. I'd therefore encourage you to check for a monsters elemental HZV before taking it on and choosing your weapon accordingly. You'll also see some elements that you probably see for the first time like Light or Dark. These are combo elements, which means they deal the damage of two or more elements simultaneously. They can be very strong if the monster has a weakness to multiple elements.
Generally the weapons to consider for this rank are either Gou or Exotic weapons. Exotic weapons are recommended for the sets above since they come with built in speed eating, and the Gou Boost isn't really utilized. If however a Gou Weapon fits a monsters weakness better it will deal more damage. Good choices would be the Shagaru SnS (Light) or the Gore SnS (Dark). If you don't feel like crafting a weapon for every element the Nargacuga SnS is your best bet since poison is also really good in frontier.
Congratulations for making it this far! Now the game starts becoming incredibly unique and a lot more fun.
Most importantly, Extreme Style is a game changer. It is the best style for most weapons including SnS. Check the playstyle section for more details about Extreme Style.
After you've equipped Extreme Style it is important to check the Leap's guide again, which will give early g-rank gear recommendations. Basically for now be sure to get the Black Orb SnS and the Entora armor from the hunter navi.
At this point progression becomes a bit unordered. To fix this I recommend to just follow the GR1 and GR2 Hunter Navi. It will reward you with progressively stronger armors and teach about some game mechanics. I also want to mention the Rain servers bounty system, especially the progression bounties. These bounties will reward you with useful materials and introduce you to Rains custom endgame. For more info on how the system works and what the benefit of interacting with it is, please don't hesitate to ask in the discord or check out the respective channels.
Once you reach GR50 you can make the Donru GX armor from the quest called Cattleya's Recommendation. With this and some decos from the Navi and possibly a bit of farming from the Gear Recommendation deco quests mentioned in the navi, you can make this simple mixset.
If you followed the Leap's Guide you will have read about Sigils. SnS has a very good Sigil called Beam Slash (SnS Tech Change). If you want, and this is not at all necessary for now, you can try to get a Beam Slash or Length Up Sigil by rolling the Berukyurosu (Beam Slash) or the Zerureusu (Length) sigil. Sigils will not be a gamechanger right now but will become a lot more important in the endgame. If you're lucky and roll a Beam Slash sigil be aware that your optimal dps combo changes as explained here.
Now your objective is to reach GR~200 to get access to zeniths.
The first thing to do as soon as you hit GR200 is trying out the zenith fights. Be sure to read Leap's guide for the necessary information up until the korinyi set recommendation.
As for weapons to choose I recommend one of these three. Poison is generally preferred if going solo and para for more road or teamplay in general. You can also choose any elemental weapon but their usefulness will heavily depend on the monsters weaknesses.
With this weapon equipped, you can get the full Korinyi Set from the shown specific Z1 Mido quest.
From there you should be able to get to floor 11 on the hunting road, which will unlock all the decos for your first zenith mixset. It is up to you if you want to road in your old donru mixset or the new barebones kori set and be aware that a team will make reaching your goal way easier.
Instead of the korinyi set recommended in the Leap's guide I recommend this set instead. The cuff is optional but the Z-skill is very good on SnS and unlocks the animation cancel.
G Furious * Assault -> 500rdp
G Furious * Blade x3 -> 500x3 rdp
G Furious * Health -> 500rdp
G Issen * Cease -> 3150 rdp
G Abnorm * Boost x5 -> 1000x5 rdp
Elzelion GN GX5 x3 -> Elzelion Twin Sac x6 (1000x6 rdp or 100x6 NP), Bird Wyvern Ringer x3 (2000x3 rdp or 200x3 NP)
Elzelion BM GX5 -> Elzelion Twin Sac x2 (1000x2 rdp or 100x2 NP), Bird Wyvern Ringer (2000rdp or 200NP)
Kirin GN GX2 -> Kirin Top Tendon x2 (1000x2 rdp or 100x2 NP), Kirin Wht Horn (2000 rdp or 200 NP)
Total: 30.650rdp, or 10.650rdp if you use NP or farm the monster materials.
At this point the Rain server starts heavily depending on the hunting road to progress your gear. Your final goal here will be to reach floor 80 in one go and kill 30 Fatalis across all your runs. After that you will have unlocked everything to make the strongest gear in the game, although you will still need to farm it.
It is very important to get 55 elemental resistance in every element while going for longer road runs since Zenith blights will cause you to cart. The default way to achieve this in the kori setup with 5 base res is: All Res +20 SR Skill, All Res +10 Road Skill, All Res +20 Guild Food.
At this point I also want to quickly mention that My Mission progress will start to matter a lot in road, so its never bad to get some level either doing the missions manually or use My Mission Tickets to skip them.
If you still struggle to get to floor 80, but managed to reach floor 50 I urge you to make a set having the incredibly powerful Hiden Skill. I recommend either one of these two options.
Now that you've made it to the endgame of Frontier let me remind you of mechanics that SnS will heavily benefit from once you finish leveling them:
My Missions: You should absolutely try to max this as soon as possible to not get your damage limited by the attack ceiling. The damage reduction it offers is also tremendously helpful
Caravan Jewel: Don't forget to finish this grind aswell, since the Perfect Defense skill is very useful on SnS. Weapon Art large is also just a 5% increase in damage which is used universally for melee weapons.
Transcendence: Often overlooked, but very strong. The buff that a max level transcendence presents is extremely good for both DPS and Survivability.
Enjoy the Road! (pun intended). All of these things you can of course do while working on an endgame set that you desire. So feel free to move on to the next section of the guide.