Starting Out & PvE
- Between level-up rewards, events, and stage missions, you'll get plenty of gems, and the single-player is a completely realized game at about the same tier as the old GBA/DS ones. Just make whatever decks and play whatever characters you want, and you'll have a pretty good time.
- Start as whoever you like more, the game isn't hard enough to punish you for that decision, and you'll unlock the other before too long.
- If you can't decide, Kaiba's starting deck is slightly better, and his level 13 skill, Beatdown, is so good and general-purpose that it got nerfed. (It's still very useful, just limited to once per Duel now.)
- Once you have other character options, you may want to look through their skills and level-up rewards lists before you commit to one; some characters can give you pretty good cards for specific decks that you can't get any other way, or have unique skills that can push a deck over the top from "okay" to "pretty dang good."
- Your first 500 gems should go towards your starting character's first/older structure deck, then 1000 into their second/newer one. After that, focus on whichever of the newest packs looks like it has a deck you might want to play.
- Prebuilt decks are also a decent place to start on something cool, but you can only get one copy of each in pure F2P. The second costs $2 of real-world money, but might be worth it to you, and the third costs several time more.
- Focus your efforts on the missions to level up your Stage at first. That's where most of the good unlocks are gated behind, including other characters, and AI opponents who don't suck.
- Your stock of generic duelists refreshes every time you level up the stage, which can be very useful for keeping a long play session going early on.
- Don't try to grind duels at the gates for card drops until you can duel Level 40 characters (Stage 30). They're more difficult, but it clears most of the chaff out of their drop lists.
- Once you can, though, grind Level 40 Kaiba for two copies of Enemy Controller. It is, hands down, the best general purpose PvE-drop card in the game, and fits into virtually any deck.
- The other series have their own characters and their own Stage levels. Great for collecting more gems if you want to, and can have some pretty interesting skills/drops. The level of generic duelists you fight carries over across series, regardless of their respective Stage levels.
PVP
- If you're just interested in the stage rewards or casual PVP, play whatever decks you like, the low ranks are mostly other casual players (and the occasional asshole).
- Rogue/budget decks can still do respectably well, but you'll probably top out at about low-to-mid Platinum unless you start getting serious.
- If you're aiming to climb the ranks, Duel Links Meta has a living gem guide (https://www.duellinksmeta.com/gem-guide/) that will give you the approximate costs of building whatever are currently the top tier decks. Go through them until you find one that interests you, then put it or something like it together, ideally unlocking and then grinding with the recommended character to do so.
- Take some notes on what you're looking for, just in case the guide changes between when you start building; finishing up a deck that isn't quite top tier any more is probably a better use of your time than starting from scratch on something new.
- Don't worry so much about the cost of tech cards at first, just find something where most of the core cards you want are in a single box. Those Enemy Controllers you got from Kaiba are just as useful in PvP as PvE.