The First and Most Valuable Purchase
This might paint the game in a bad light, but as a new player, it's important to decide from the start if you will be fully free-to-play (F2P) or if you're open to spending some money. Most offers are poor value for your money, but there's one limited-time offer early on that can significantly impact your game. Initially, you will get an offer to buy Commissar Yarrick, but if you wait for it to expire, you'll receive an offer for the best support character, Isabella. She is the best healer for the Imperial faction and will help you in all game modes. If you're even considering spending a few bucks, this is the best offer to take.
Find an Active Guild
Look for the most active and full guild you can find that has requirements matching your power level, and try to join. Once you're in, stay active and do your best in both Guild Wars and Guild Raids.
Guild Raids
At the start, you won't deal a lot of damage to raid bosses, but your guildmates will. You'll still earn Guild Credits, which you can spend in the guild shop. Initially, focus on unlocking characters required for campaigns — Archimatos, Boss Gulgortz, and Eldryon.
Guild Wars
Be active in guild wars, even if you feel too weak. Try to spend every War Token because you'll earn 50 War Credits for participating in a battle and 20 more for every kill. So even if you can't get any kills, playing all 10 battles will still earn you 500 War Credits.
Currently, the only thing you should spend your War Credits on is Nauseous Rotbone shards. He's the only Chaos healer, and he'll be invaluable in any game mode where you can use him.