Since you have access to the Eater of Worlds raid lair from Curse of Osiris, I'd suggest trying to get into a group for that first. It's shorter than Leviathan and in my opinion easier for a rookie to pick up. Playing as a Voidwalker using the Devour tree will help keep you alive while you get familiar with the mechanics of each fight. As for gear, I'd encourage you to bring a variety of weapons so you can fight at both short and long range. For example, if you love using SMG's, try to pair one with a scout or longer range pulse. For power weapons, cluster bomb rockets are useful in just about every situation (just remember to not blow yourself up). Something else to consider is the mindset you bring to a raid. As a rookie, there will be plenty about each fight that you don't understand - that's expected. Don't be afraid to ask questions. A good team will help coach you, but even the best teammates can't read your mind. If you're confused about something, speak up. Finally, if you have a group of friends who have also not tried a raid yet and are interested, going through it "blind" and figuring out how to complete each encounter by yourselves is without a doubt the best way to experience them. I understand that might not be the case for you, but once you spoil an encounter, there's no way to have it un-spoiled. Think about it before you look up guides online.