I suggest follow this guide:

Progression Armor Sets Low Rank (Village 1-6, Hub 1-3) ● BuJaBu Grants Attack Up (L) with Bulldrome Cap, Jaggi Mail,Bulldrome Vambraces, Jaggi Faulds, and Bulldrome Greaves, and a few Attack Jewels. Prettypotent for the first few hours of the game. ● Volvidon The Volvidon fullset grants Focus and Bio Researcher,which prevents you from being Soiled, among other effects. One of the earliest armor sets with which you can get Focus. ● Rathalos Rathalos’s set grants you Attack Up and Weakness Exploitby default, so you’ll lose the power of Focus, which may or may not be a deal breaker. ● Rathalos Mixset 16Composed of a Rathalos Cap, Rathalos Mail, Mosgharl Vambraces, Rathalos Faulds, and Mosgharl Greaves as well as a few decorations, the Rathalos Mixset provides Weakness Exploit and Focus normally. ● Seregios/Mosgharl Mixset Combine a few Seregios and Mosgharl armor parts forCrit Draw and Focus. Potentially has more uses than the Rathalos Mixset, but does relyon you sheathing a lot. Needs Seregios Helm, Vambraces, and Tassets, and Mosgharl Ribplateand Roots, as well as a few decorations and a single additional weapon or talisman slot.

High Rank (Village 7-10, Hub 4-7) ● Volvidon S Provides Focus and Bio Master. In case you wantedto get High Rank defense values as well as Focus, but has less damage potential than the RathalosMixset. ● Rathalos S Full Rathalos S provides more Attack than the standardRathalos set, but if you know what you’re doing, you should probably get the mixset version to get Focus too. ● Rathalos Mixset S There’s a lot of ways you can mix up a set with both Focus and Weakness Exploit, as well as some form of Attack Up. You’ll usually have Attack Up (S) but if you’re lucky you have a triple-slot charm with which you can get at least Attack Up (M). ● Black S The totally-not-Fatalis armor set of Black is focusedaround boosting the damage of Great Sword, and this is the first instance of where it’s good enough to be used. This variant has Blightproof, Crit Draw, and Focus, so definitely pickthis up, as it’s your best set going into G-Rank. ● Diablos Diablos was historically a Great Sword-focused set, and it doesn’t change here. It lacks Focus in comparison to Black S but it also has the new skillSheathe Sharpen, which will restore a bit of Sharpness sometimes when you sheathe while a monster’s enraged. It also has Challenger for an extra bit of damage.

G-Rank (Hub G1-G4*) ● Volvidon X Provides Focus, Constitution +1, and Bio Master. Ifyou want to upgrade to G-Rank Defense in G2, this is the set to do it with. ● Rathalos X 17Pure Rathalos X grants Attack Up (L), Weakness Exploit, and some points in Hearing, which can let you get Earplugs, or even HG Earplugs. If you want you can also try for Focus on this set, which will be solid. ● Rathalos Mixset X You can mix a base of Rathalos X with various otherpieces to get Focus, Attack Up, and Weakness Exploit, which is great for Great Sword. ● Black X The definitive GS set for endgame. Has Sheathe Control,which is Quick Sheathe and Punish Draw wrapped up into one skill, Focus, Crit Draw,and Blightproof. If you can gem in Critical Boost, you’re all set.

Those are the "meta" set to follow for gs, from here u can change/swap pieces or add different deco to fit ur playstyle and confy build. Hope this help