Tangible Things

It's much easier (and far more enjoyable) for players to see physical objects, than to comprehend and parse information.

Try to represent the game state and information with pieces, which are either in play or not in play, or at a particular place. Avoid representing the game with abstractions like text. Numbers are much more information-dense than text, but still use them sparingly.

The components are the game.

Imagine a card that has text that says "Unique Creature — Minion Fire Shadow Berserker" and has five different attribute scores. It has the ability "Other Shadow creatures you control get +1/+3". I'd rather the same complexity be spread out over five simple cards. Instead, I have a Wizard card with three spell tokens on him, I have an elf with strength 3 and a sword card, and I have a horse token.

Types

In games centred around cards, you usually need a few card types (like "Creature" or "Item"). These types behave differently.

Avoid subtypes (like "Elf"), factions, and other arbitrary categories with no inherent behaviour. Avoid making things that care about such categories.

These categories are not tangible, and often arbitrary.

If you want to add complexity, add more objects. Do not make the existing objects more intricate.

Use many simple pieces.

Theme and psychology

Tangible objects are also much more thematic. Each can be given art, design, location, size, and shape.

People also want to manage physical objects.

In my farm game, the trees grow, by adding tokens. The bandits spread out from their ominous fort. The fish eggs flip over into fish. Most of the game is tangible. The playtesters love this tactile engagement with the game.

You'll need some systems that are intangible, but minimise them.