Super Divers is a friendly game to enter and a demanding one to master, and the gap between those two states is almost entirely timing. Here is the route that works.
Do not buy cards before you have played. Take a Trial Diver Passport from the machine — free, up to 30 uses, and it can be transferred to a full Diver Passport later, so nothing is wasted. Play Challenge Dive and Arcade Mode first, because both teach the strike battle without the pressure of the ladder.
The single thing to practise in these first sessions is the timing of the strike battle presses. It is the only part of the game that does not transfer from knowledge of cards, and it is the difference between winning and losing a fight you should have won on deck strength. Everything else — the rarity tiers, the card lists, the modes — you can learn from a guide. You cannot learn the timing from a guide.
Your deck is seven Battle Cards plus one Avatar Card. Until you have enough cards, the machine fills the gaps with virtual cards, so you can start with a partial deck and fill in as you pull.
The beginner's deck should prioritise three things over everything else:
Do not chase the newest God Rare with your first purchases. A normal card with a useful effect will win you early matches, and matches are how you learn the timing. Buy the cards you need for a working structure first and the chase cards second.
A practical order of operations: Arcade Mode and Challenge Dive to learn timing and mechanics, then History Dive to broaden your character pool, then Casual Match to test a new deck with no rank cost, and only then Online Rank Match during the daily 10:00–23:59 JST window. Add Strike Battle Rush along the way — because card effects do not matter in that mode, it is a clean place to sharpen your timing with nothing at stake.
Two things that provoke a lot of unnecessary anxiety for new players. First, losing points and ranking down are part of the system — the game explicitly supports it, the Bronze 5 beginner support bonus exists to smooth the early climb, and the season reset means your final rank carries forward rather than being lost. Second, the arcade scene is welcoming: store tournaments, venue events and the national championship exist to bring new players into competitive play, and the physical nature of the game means your local regulars are the people you will actually meet.