It's good to see more people playing Gen 3. The most important thing for every team is to have an answer to Dragon Dance Tyranitar. Good answers to it are Swampert,Flygon and bulky Metagross., see Tar analysis for more details. Every team should have a reasonably bulky pokemon who resists rock to beat DD Tar and Aerodactyl. You also need a way to beat teams like this one:
https://pokepast.es/7fdfe726cd7bb492, with Tar,Skarm,Bliss,Pert,Gar and one free slot.
VR:
https://www.smogon.com/forums/threads/adv-ou-viability-ranking.3503019/
This video is a great starter guide to adv as well:
https://www.youtube.com/watch?v=8EkwMYi_BzY
This thread is great to learn the various styles of teams:
https://www.smogon.com/forums/threads/adv-ou-teambuilding-strategy-archetypes-and-cores-a-data-driven-approach.3654874/.
If you have any team request, feel free to ask